Need help determining next upgrade - 3rd ATTEMPT

Unless they're designed that way, your speakers also look very close to the back wall.

One thing I'd do before I started spending money was to make sure that the fault isn't with the recordings themselves. If you've heard those exact same recordings on other systems sounding great, then you know it's possible to make changes and get improvements.

Another speaker placement method. Keep in mind all these methods are starting points. Quarter inch incremental adjustments can make significant changes at the listening position

http://www.cardas.com/room_setup_square.php

Equipment changes before speaker placement tuning is not recommended.

I agree with Al thet the "room treatment" or "speaker positioning" remedy can be easily tested by listening to the offending recordings while sitting closer to your speakers..."nearfield" as they say.

If digital, you can currently pick up a Pangea audio ac14 se or ac14 power cord for your DAC depending on the one currently in use, for well under $100. Using a power cord like this designed for digital source applications can probably only help and not hurt.

I am noticing improvements similar to what you seek since applying the ac14se with my mhdt Constantine DAC. I did the upgrade needing to replace an existing damaged power cord and knowing that I have greatly improved performance of my setup in the past by systematically shielding against EM noise.