The Law of Accelerating Returns

"As for price, you are not going to get top quality sound from a $500 tt or a $700 dac. $7k for a dac, $10k for a tt/cart/tonearm, now you are getting into good sounding gear."

Pay more attention to the quality of engineering and design implementation. Most importantly listen with an open mind and let your ears be the judge instead of the price tag, unless bragging rights and status is all that really matters to you.

Yesterday I adjusted the crossover setting on my subwoofer and changed its position relative to the front wall. Let's say the crossover adjustment applied about 50 cents worth of time and effort to a $20K system.  The bass response  improvement may not have been as great as adding a subwoofer in the first place, but then, the cost was far far less. 

However, the "law" won't necessarily apply if you just start fiddling with dials (or spending money). You first need to identify where your system needs improvement (for example, in the sounds of kick drums.)  

Helmholtz treatment "only" work on ONE frequency and to bring down a peak in that very specific frequency and nothing more or less.

NO! they can be used to notch around a frequency. To contour a particular frequency or by using slot vs tube vary a single resonator to encompass several frequencies with less control but over a much wider bandwidth. 

Helmholtz is the ONLY way to tune a room completely. 

I've even used passive radiators as frequency collectors vs frequency producers. 

The concept can be used to increase a given frequency by notching around it and lowering the over all SPL. I use several different resonators and  two huge 100+ cubic foot pipe collectors. It looks like a pipe organ turned sideways in both corners of the front wall, floor to ceiling 36 x 36 x 96" but they are behind the wall. Different diameter ABS tubes are sticking out of the wall.

Many of the tubes are capped, about 1/3 aren't, the ones that ARE capped are used to diffuse, the ones that are not, are used for tuning. You simply push or pull them further in or out of the wall. You pick the correct size 1/2" - 6" pipe uncap it and tune it. I also use 4 more adjustable tube traps for the rear and sides, with slot style wall resonators for fine tuning.

You can hear a fly fart if you want.. :-) I think that would be in the 18khz range.. LOL

10hz to 15khz 100% tunable..

BTW ALL the traps on the walls and floor are decoupled from the wall and floor..

Speakers, Subs, and any object with equipment on it.. (Especially TTs) are decoupled. A sound changing experience for life. The same for servo driver systems and small planars.. A different sound that is very appealing to me..

Equipment? Gear? Take your pick and go from there. After the ROOM everything else is pretty superficial. All those thing that did make such a big difference before don't amount to a hill of beans.. 10K integrated means squat then, when a 2K total system will sound better. It's the room and tuning it along with decoupling and refining the quality even more.

Did I mention electrical? :-) This is when "Doris get's her oats".

Room tuning may be something an obsessive/compulsive listener could chase around until they're ready to gloat about it (I think rooms generally can add a sense of realism with only furnishings and regular stuff, unless maybe your room is an abandoned shipping container), or not. What anybody likes or doesn't like about the sound of a system is utterly due to personal taste, and in my experience that seems to vary wildly. My current system of relatively modest items chosen and kept or rejected and replaced, seems astonishingly better sounding than any I've heard anywhere at any price mostly because it's there by and for me. I hear some interesting improvements from cables or amps getting their legs after break-in, but that's simply fun and not a huge deal. Unless I need to gloat.

Can Helmholtz resonators trap hot air?