Can a DAC sort out a flat\cold amp?

@bobby1945 

All great ideas Bobby.  OP should implement all.

This post just goes to show what a mess you can get into down the digital rabbit hole.  The faults being heard are almost certainly due to digital issues and like most here I would exonerate the amp.  But adding a digital equaliser won't solve the problem.  It's sending a spider to catch a fly.  Just adds to the mess.

Like Bobby says clean up the whole system and simplify.  Where possible put individual components in other systems to verify they operate correctly.

That amp could easily be sold here or on ebay. It is or was a popular Amp. Maybe it would do better paired with a warmer speaker. You may just have a synergy issue. You could also try a tubed dac such as the Border Patrol r2r dac. It may warm it up a bit. Cabling can also be used to tailor the sound. If Possible, leave that Amp on continously for a week. Maybe it will burn in more.

Thanks for the pic.  It tells everything.  It's your room and the positioning of the equipment therein where the problem lies.  A 1,000,000 dollar amp won't fix that.

The room looks frigid. How to warm up the sound in there with equipment only is a mystery to me. Major reflection effect with that setup. My ears are ringing just seeing it, and not from my tinnitus. The boom box sounding better in the middle of such room makes sense. Work with the room and setup first is my two cents.

The room will be a mess, but I don't think the speakers in that location nor even the reflective surface are going to result in too little bass. I would expect boomy bass from the near corner placement.

Something is broken. One of the speaker polarities wrong, bad amp, etc. Replacing the speaker cables, using Roon (except for equalizer which you can do much cheaper), interconnects, DAC, and a bunch of other things is not going to make any difference. Find out what is broken and fix it.

Buy a microphone and learn how to measure your setup, then you will not need to guess.