Best return for the money, system upgrade suggestions please.

Room acoustics, if you don't have that done, is your best place to start.


Otherwise your DAC.



Best,
E

The best one on your list is the dedicated AC line. But even then only if its DIY (otherwise, electrical, too expensive, poor value) and you're the homeowner AND you'll be there a while. 

Otherwise you want to look for things that will:
1. Be permanent. No obsolescence. Never wear out.
2. Be used your whole life regardless of equipment upgrades.
3. Actually be appreciated more and more as time goes by.

Everything on your list is a fail by these outstanding criteria.  

What does pass the test:
1. Pay down interest bearing debt.
2. Synergistic Research ECT and HFT.

There's a reason they're in that order. Don't be a slave to debt.

Pay down your debt! That's the number one thing you should always do with extra money. Later, you can spend on toys. Enjoy the system you have now.

I recently added a second subwoofer.
A second M&K Mark 2       8” sub.    Discover Deep Base
I had one originally I purchased 17 yrs ago  had it wired to a separate 5.1 theatre.
Found another one on eBay $160 delivered ,swapped out a 10” from
my two channel set up. Swapped in the two 8” m&k.
Sounded good w one  10 “sub,  But fantastic with  the two M&K 8”.
Deeper Tight Base immediately noticed.
Midrange seemed much better also.
Best low  dollar, night / day difference low cost I’ve ever done.
Something about those original m&k subs makes them very good design
The  MK  8” subs replaced a much more expensive  10” subwoofer previously on the 2 channel ,10”,now in the 5.1 system

System details are in my virtual profile

R