if you had this system, what would you do to make it sound the best you can

Yes on all of the above. McIntosh is very warm sounding. Silver interconnects from your source to your McIntosh. I agree, ditch the equalizer... more wires to contend with. 

Upgrading the fuse. Makes a difference! Yes on a power conditioner. A used Niagara will lower the sound floor. Sort of the difference between driving in your car with the stereo on versus, sitting in your driveway with the music on. 

If you keep the speakers, a sub will make a huge difference. 

It's unfortunate, but Everything makes a difference. Only your ears can make you a believer. 

My system, Lumin T2 streamer,-- AQ Wel xlr --McIntosh MA 12000 with purple fuse--AQ Firebird speaker wires--GR Research NX-Oticas speakers with two Double trouble subs. 

I also just added a McIntosh MEN220, room correction unit. That unit made a big difference and balanced not only the room, but also the phase and the frequencies between my speakers and the subs. Impressive difference.  

Panamax power conditioner should go. I have one and don’t use it in my System, it tends to be restrictive.

What is size of room which really impacts Quality of what you're hearing.  I would for more powerful amplifiers, mcIntosh is fine

I suggest taking some of your upgrade budget and attend an audio show. AXPONA is coming up but there are shows all over the country now. There is no better way to get an idea of how your system stacks up against what is currently available.

I could easily post the same question you have but I don't need to. I'm running a late '90's vintage system with Krell amp and preamp and Thiel CS6 speakers. When they were new they were solid Class A. I've been to three audio shows (AXPONA, Florida, PNW) and I found out that my system holds its own against most of the six-figure systems I heard. In many cases my setup sounds clearly superior to systems where the cabling and power conditioning cost more than my entire rig.

You will hear lots of speakers and some of them will tickle your fancy (I think the rest of your system is fine). You will see that high end speakers sound REALLY different from each other and what you like may be the opposite of what someone else likes. At the 2018 AXPONA they had a pair of large Wilson speakers in a well appointed room and I thought they sounded like fingernails on a chalkboard. Other people I talked to thought they were the best sound at the show. Once you go through this process you can narrow down the choices and make an informed decision. And besides, it's just plain fun.

8th note agree 100%. Also I would like to add cabling make a difference but you have to experiment yourself.

I would certainly agree with upgrading from the Spendor A5s (48 Hz to 20 kHz) to a pair of floorstanders that offer great SQ of a more extensive frequency range, reaching down to at least 30 Hz (-3dB). There are many affordable options available that won’t break the bank. If a floorstander only reaches the low registers around 50 Hz, one might question its purpose. The Halfman iron rule suggests that a larger cabinet could allow for a fuller and more enjoyable sound across the frequency spectrum. So, why not opt for a floorstander that offers a more comprehensive range? Your electronics are fully capable of supporting it.