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

If Iam not mistaken Audioquest has the diamond model for the Ethernet cabling.

@robert1976 yes the TWL Obsession are good cables with excellent connectors. 
@verdantaudio provided some excellent thoughts on DACs and streaming with Roon.
I would also throw in trying a good Ethernet switch, as well as to try and upgrade Ethernet cable from wireless access point and or switch to DAC. I noticed a good improvement when I switched from standard cat5 to Supra CAT8 just as an example. 

@verdantaudio thanks for explaining. So if I’d get a Lampizator Pacific or Aries Cerat Kassandra, or any other DAC that isn’t a Roon endpoint, I have to connect over USB. This will turn my Nucleus into both Roon core server AND player, which causes performance to drop. This may even undo the positive effect of using a better DAC?

Moving to a non-Roon endpoint DAC means I should get a separate player? Meaning Nucleus > Player/renderer > DAC?

What player/renderer should I look into? This machine will not have storage space for local files and not run Roon core operating system correct?

You are absolutely correct.  Move to a DAC that is not Roon Ready and using Nucleus as renderer and player might actually deliver a regression in sound with the upgraded DAC.  These are the best players I have heard in descending order in terms of price:

Antipodes Oladra or K50 - these are server, player and clock solutions that are not inexpensive but will deliver elite levels of performance.  This is the sort of elite solution that would be at home in your system.  $25K or $17.5K respectively

Antipodes K22 - Clock and Player portion of K50 and can be paired with any server.  $9K

Weiss DSP 501/502 - this unit has a variety of DSPs including room correction.  There is an argument simply adding this in the chain and applying a DSP would resolve your issue with 100% certainty as either the d'esser or vinyl mode would likely add the warmth you are looking for.  $7.5K/$8.5K

Bricasti M5 - this is a pure player and is an awesome value.  Nothing fancy.  No DSP.  Just a high quality player.  $2400

Chord 2Go/2Yu - This is particularly interesting due to its high level of flexibility and wireless capabilities.  That being said, it is not at its best via Wireless.  It is at its best wired and is equally good compared to the Bricasti M5 via Coax though harder to setup.  $2240

@deludedaudiophile I tried that and Roon’s equalizer distorts the sound to the point I can hear the difference. Piano sounds off, for example. Having a highly resolving system is a two edged sword.

Looking at the Stereophile revies of the Audionote DACs, one thing they are not is resolving. Don't get fooled by the price. From what I learned of acoustics, your lack of absorption will also greatly reduce the resolution of your system. Perhaps Roon does have issues with its equalizer, but I have not found that the case and that does not seem to be a comment I have read. Good headphones may not have perfect frequency response, but they are far more resolving due to their very low distortion. If you were trying to use Roon with the Audionote, that may have created issues due to the Audionote's simple architecture. You may be better with a low distortion DAC and using Roon in your particular setup.