How good can it get, really? - my stereo sounds amazing!

I really love my stereo currently. I keep thinking I should be looking for the next piece to upgrade - phono stage, stereo subs, etc., but honestly not sure what to change or why I’d potentially spend more money to achieve a result that’s lesser or equal to my current sound quality. I sorta feel clueless as to how to proceed without screwing up what I have. I know it can get better but honestly I’m at a place when I just don’t know how it can. Hmmmmm.... not a bad problem I guess. Open to suggestions for sure. Thx.
My suggestion is, enjoy your setup. Stop reading stereo magazines, which are designed to make you want stuff. Stop reading audio bulletin boards, which can cause fear and doubt. Just enjoy the music, and count your money!

When you stop enjoying it, take 2 weeks off and see if that helps.
This is a difficult question to answer since you did not post what it is you have for a stereo system. You might have some wonderful pieces, or you might have some items that could use a change. Again, difficult to answer.
IMHO, far too many people go cheap on cable. It is often difficult to look at "wire" as a piece of equipment, and it is not as "cool" as some huge amp, or a preamp with zillions of tubes sticking out of it. But something has to carry that signal from one place to another. So, it you think your gear is up to the task, then start looking at cables, especially power. I know that nothing gets a good argument going like the word(s) cable, or wire, but trust your ear and not something that someone tells you is "snake oil". There are a lot of good power cords out there and a lot of free trials. Break-in can be a bear but if you have good revealing equipment now, better power cords will really surprise you with their performance.
Of course, we can all appreciate the desire to "change it up", without knowing what you have currently, it's impossible to give you any suggestions.
Post removed 
LOL! Ha! Very well put dweller2! And I will add another thing that my financial adviser likes the say and that is "Act your wage"...
Air ionizer?
Schumann resonator?
fo.Q tape?
Perfect Path Technologies and Synergistic Research products?

Get curious.  Improving sound quality can mean building
upon what you have already assembled.  There are many discussion threads that can point you in different directions; learning from others may be helpful...
Thanks for the responses. I like the idea of upgrading my power cables but not sure where to start. I definitely don’t want to spend a fortune in cables but am willing to pony up some.

Here’s where I’m currently at: 

Rogue Audio Cronus Magnum II - tubes rolled from stock JJs to Gold Lion 12AX7 and 12AU7s with a Brimer 12AU7 in the center position. With running the Phonomena II+ preamp, I'm not sure if I'm even utilizing the tubes anymore? I upgraded the Phonomena to accommodate the Hana SL Moving Coil cartridge. My turntable is a Clear Audio Concept table. Speakers are B&W 805d3 stand mounts with a REL T9i sub. Kimber Kable speaker and interconnects. 

A little note of encouragement from a reviewer of 13 years:

Stop being such a chicken! Scaredy cat! MMnnnnn - phooey! ;)

There are many more levels of sound quality improvement than you can imagine. You are not close to the ultimate.

For instance, as a thought experiment, imagine spending time in your home with some of the major genres of speakers - panel (magnetic planar or ESL, horn or horn hybrid, line array, etc. Just considering the different genres of speakers and the potential for improvement, you are far away from the potential that systems have that may sound far better to you, literally dozens of levels of sound quality. Frankly, there are more levels of sound quality available than audiophiles will experience. That is true for nearly all audiophiles, myself included. The odds are very good that you are nowhere close to your dream sound. Just because it sounds terrific to you in no way means it cannot get much, much better.

For instance, if you were to switch to a floor standing speaker, there would be many potential improvements associated with that move alone.

Keep a notebook of your current favorite system from first power cord to speakers. Make changes, and if you don’t like them, revert.

BTW, if your first priority is to not spend money, then pay a lot of attention to burn in, and tweaks. That will keep you right in the same performance zone, but you will have saved your money!  :) 
There is nothing - repeat - NOTHING wrong with your power cords! To believe otherwise is to be caught in a neurotic obsessio! Ditto for your interconnects! 
Wire has become a lucrative market for the unscrupulous to prey upon the gullible. Tweaks and burn-in? LOL!
You guys, I am absolutely enjoying my stereo - as stated above, I love it! I’ve been living with it as-is for about a year now and still love it. I listen to it every day. 
I recognize that just going to floor standing from stand mounts would change things (likely for the better) but maybe not? I’ve read that the 804d3 is actually less detailed because of the two in cabinet woofers vs. the 805d3. I wonder if trying a second Rel sub is a better route? I agree - I just need to experiment a bit. Or maybe I go back to an all tube phono stage? So many options for sure. 
If you're happy with what you have, that's awesome!  If you want to take it to another level, add another sub (or 2 or 3).  You'll get a lot more bang for your buck out of that than buying expensive cables.  Not that they can't help, but whatever improvements (if any) you get from cables will be subtle, at least to most people.  Adding more subwoofers, especially if you have four of them will be more than a subtle difference.
Most audiophiles are habitually discontented, or only happy when engaged in the next hunt, but not when it's over.  If you're truly content, don't for heaven's sake rock the boat.
Four subwoofers is definitely not an option for me. I have one currently, which I’ve hidden from sight. I actually don’t like what “gear” or stereo equipment. I love minimal, clean layout and interfaces. I love analog. 
There’s a lot of unmapped territory out there regarding RFI/EMI and how to deal with it. It’s like Chicken-man. He’s everywhere! He’s everywhere! 🐔 🐔 🐔 It’s generated by electronics, room purifiers and other appliances, Coming through the house AC, not to mention all the TV, radio and cellphone transmission coming right on through the windows! Hel-loo!
Post removed 
As a good rule of thumb, you should spend four times what you pay for the entire system in wire elevators (ideally, nano charged ceramic versions burnt in for 2000 hours) and another 4X in power cables to cover the last meter of electricity after the electricity gas travelled 500 miles previously. 
LOL - yeah that’s sorta how I feel about power cables, ceramic elevation discs, etc. I don’t do any of that and have entry level Kimber speaker cables and interconnects. Funny. 
I'm in the same boat so to speak, as far as really liking my current rig...I also think understanding something about why things can sound great without being stupidly expensive is key...great design is what it's all about, and I use some "previously owned" items that have turned out to be astonishing bits of kit, as they say. It's also important to see beyond the proponents of snake oil tweaks as that stuff just muddies the waters.
mahgister had an excellent post recently on this very subject, which I agree with so well I will now shamelessly steal from. For all the near infinite amount of gear out there it all can be divided into three big categories or classes- budget or mid-fi, expensive, and cost no object. Most of us are in the big middle range.

Now here’s the thing. Within these ranges everything is pretty close in performance. Close enough anyway that working with what you got is a whole lot more cost effective than upgrading.

I learned this decades ago, which is why I agree with Mahgister on this. A $60 set of BDR Cones improves the performance of a CD player better than "upgrading" to a $500 more expensive CD player. A $500 Synergistic power cord will make it sound like a $2500 more expensive CD player. Throw in an Orange Fuse, slip an Omega E-mat under it, now it may not even be possible to find a better sounding player. Sitting on its factory feet with its factory fuse and factory power cord, I mean. Its that big a difference.

But the tweaks don’t have to be expensive either. Anything that gets cables up off the floor will be an improvement. Electrically insulative materials like ceramic insulators work the best, but anything is better so it costs nothing to try and see. Best of all this like many tweaks does not alter your systems precious balance. The good ones simply give you more of what you already have.

Omega E-mats and TPC from Perfect Path Solutions, Synergistic Research HFT, ECT & PHT, Cable Elevators, even things as simple as carefully routing cables to avoid tangles and coils and running close parallel will make a noticeable improvement.

The beauty of this approach, besides getting you off the upgrade merry go round, is it all works with whatever you get if you do finally upgrade something. Do everything mentioned here and you will be amazed. Your system will be transformed, and yet without giving up any of the qualities you love so much right now.
I don't think I've seen any mention of acoustic treatments. Is your room "tuned" at all? Perhaps look at some "art panels" (artwork over acoustic panels) at the first reflection points if possible, or some bass traps in the front corners. I gather (and can appreciate) that you don't want your system to shout "look at me", but it's possible to get acoustic treatments that can provide a noticeable improvement (potentially even significant) while still fitting into your decor.

That said, if you are enjoying your system as is, why mess with it. 
Post removed 
I don't think I've seen any mention of acoustic treatments.

Omega E-mats and TPC from Perfect Path Solutions, Synergistic Research HFT, ECT & PHT, Cable Elevators, 

HFT. Guess you must have missed it.
Some straightforward advice here. I like it. I’m gonna get a second sub to see how that changes things. Can’t wait!
If you’re thrilled with your system- STOP! You are done. Buy music 

I reached the point of being thrilled 4 years ago. Since then the only $ I’ve spent on my system has been to service a 40 plus year old tuner. 
Zavato, I hear ya. The only thing I’d like to explore is going back to an all tube signal path and stereo subwoofers
The answer is almost always your room. If it is not your room, then the answer is likely your speakers and how they interact with your room. Maybe it is your amp in combination with your speakers, and maybe you have screwed that up with a speaker cable that attempts to do something unneeded and screws up other stuff in the process. If vinyl is your poison, then it could be your turntable setup, but ... see above.

I think most people are on endless tweak searches because their acoustic fundamentals are lacking. People with well designed rooms with accurate neutral speakers tend to be "happier" than those without ... and usually just listening to other people's system, or a visit to a dealer showroom reminds them how good they have it.
Buy three aftermarket power cords and put them into the system one at a time. Maybe you will learn something.  

Um, if it ain’t broke... don’t fix it? At some point contentment has to settle in. “Looking” for things to improve when things are just find is a rabbit hole at best, and can be an expensive rabbit hole that may not achieve anything at all. As said, stay with it for awhile, be in Zen mode. Nothing wrong with that. If the time comes, maybe look at a major change. New amp, perhaps separates if running integrated, or just keep what you have as your “forever” setup... nothing wrong with that either. 
If it sounds amazing, then spend your time enjoying music.

My upgrades in the last 18 months included a new DAC/power supply, interconnects and new speakers. I consider them 'end game' items for me, and will be unlikely to replace them.

Have since embarked on a journey of tweaks and their effect on sound. Some turned out to be excellent, some good, some uncertain.

My system is sounding fabulous, and is exactly what I was hoping for.
First climber: WOW! What a view! Being at the top of Everest ⛰ makes me feel like I’m King of the World! 

Second climber: Hey, get a hold of yourself! We’re only at Base Camp ⛺️
+1 geoffkait

At this point my adage is apropos:

The greatest impediment to advancing an audiophile system is the audiophile. 

For about five years I was on a tear, upgrading this, changing out that, and I've reached the same point, really enjoying the sound quality of my system, being more "relaxed" about being an audiophile, enjoying the music.
Respectfully submitted, and really not looking to argue, but I think that one large impediment to advancing an audiophile system is having something more important to ones life to allocate money on.

Also, I just watched the zero fidelity you tube video where he makes the point that before you can decide where you want to be on the audio system level spectrum, one needs to realize that it is impossible to create the sound of a live event. Once you realize that, you pick the "fake sound" (his words) and equipment level that caters to your taste. It will always be the reproduction of music, not the creation.

If one wants to dedicate "x" amount of time and money to achieve his/her brand of the best sound possible, that is his/her decision, but to judge others who can be satisfied with the tone they have achieved is IMHO misguided.

That said, I do have seven amps (LOL).

Your imperfection is in balance. Upset that balance and you’ll be on the upgrade merry-go-round chasing the memory of happiness lost. Proceed at your own risk.
Jetter you are spot on about reproducing live event...

My only question about my own stereo system is  is it relatively natural timbre sounding? and is it  there, when listening, a 3-d holographic stage ?

And yes wlutke all is about some balance...I was lucky, all my almost all homemade tweaks in the last 2 years has driven me toward a better balance...

Then the most important point is stopping to buy and upgrade at a certain point of your audio history, because all good stereo system are all that : good,but the owner most of the times does not know that himself because his room-house-audio system is not cleaned nor efficiently treated against noise etc...And thinking about taking in your own hand, at low cost, your own listening experiments to gain Nirvana is the key...I am there...

Happy New Year to all and to you....
Who would want the live event? The live event in most cases sucks. A good home system is better. It’s one of those old wives things.
If you have furniture in your listening room you can ignore room treatment as many hifi music fans do. If you have logic in your brain and reasonable listening chops you can also ignore pretty much everything sold by SR or Perfect Path or any other fringe tweak company, again, as the vast majority of audio geeks do...then, once you've come to a place where you're enjoying the music coming at your ears, you can just buy more of that and relax knowing everything's fine.
Furniture is not a replacement for room treatment. It can even make things worse.
The quality of your ears, in relation to home stereo, is limited by the best system you have ever heard. Before you hear a system that is a revelation you dont really know what you are missing, nor how your home system compares. 

When respondents get on this forum telling you to ignore cables, tweaks and room treatments take a look at their systems and then choose if you should listen or ignore. Many enthusiasts have already made a decision about such things and any communication with these members is casting pearls before swine. 

Like audiozenology states, furniture is no substitute for room treatments. FACT!