Which DACs are known to be sweet/rich/relaxed?

Going back to the suggestion of cables - I can really recommend Sommer Epilogue, XLR or RCA.

It’s a really high end construction, but bargain price. It really helped me achieve a smoother & richer presentation, but still just as detailed. The change was not subtle. Epilogue is used in High End studios and also with B&W for their testing for 802D speakers etc.... so really worth a go for the cost of entry.

I have had the Mola Mola Tambaqui in my system and this would be my suggestion before you consider switching DACs.

"sweet, rich, relaxed"

I don't think these characteristics are likely to be found in a digital system.  Perhaps in a very high 64/256 recording, just maybe.

The DAC is the bad elephant in the room.  Every time you think you have a good digital recording the DAC goes and spoils it with dither and clock errors that cannot be rectified.

Once you have converted actual sound to digital there is no way back.

R2R and Denafrips....the only way to go....OR I just picked a Shiit DAC for bedroom system and it's fing fantastic.

https://www.mcintoshlabs.com/products/new-products/MCD12000

I am surprised that, for a $12k Dac/CD player, its Dac section does not have I2s input and its player does not have I2s output...

Big learning moment!
To see what the impact of my large, mostly untreated living room is, I decided to drag my 374lbs / 170kg Stella Utopia speakers to my bed room :)

I put a few mattresses and diffusers up against the wall, rug on the floor, thick drapes behind the listening position, etc. Photo here: https://ibb.co/PNCzHnW

This well dampened environment made ALL the difference! Old recordings and playing loud no longer caused any harshness or brightness. Room wasn’t dead either: RT60 was around 400-500ms, about half of my living room.

This reminds me that the room is one of the most important components in the chain.

My 13 x 20ft / 4 x 6m bed room is obviously too small for these huge speakers to spread their wings. But it was a great way to prove a point.

This finding prevents me from chasing different gear. I’ll either install more absorption, or simply accept that a large, mostly untreated living room has its down sides.