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

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. 

@verdantaudio you said earlier:

Best upgrade from a Nucleus for people connected via USB is not to get a higher end single box server but to get a separate player renderer.

The reason you’re recommending the single-box Antipodes K50 is because internally it’s devided into two computers: one for Roon core server, one to play/render the music file.
Should I look at Pink Faun 2.16 (ultra) too?

Upgrading to a non-Roon Ready DAC comes with the additional cost of a separate player/renderer, or upgrade to 2-in-1 box like antipodes K50.

BTW, the Lampizator Pacific can be configured with a Roon Bridge (although I’m not 100% sure if that means the playing/rendering is taken away from the Nucleus and into the Pacific).

That is correct.  The Oladra or K50 have two computers in one box (with separate power supplies) along with an elite clock.  

My understanding is the Pink Faun Ultra is very, very good but their top performer is a "double ultra" which is $47K which is one Ultra as Server, one Ultra as Renderer.  With Pink Faun, it is all about the clocking and they have superior clocking to just about everyone.  I am considering adding Pink Faun as a brand but haven't personally demo'd it yet.  

I work with the North America importer for Aries Cerat and Pink Faun and I know they work well together. 

If the Lampi Pacific has a bridge available that is great.  I do not know how it compares to the others mentioned above.  I will say this.  I feel that Antipodes K50 player and clock outperforms the Weiss Player in the DAC 501/502.  It may be that that K50 (or Pink Faun, etc..) might outperform the network bridge in the Pacific.  

I still say the Trinnov Amethyst would be your best investment if you’re determined to spend $25K. You can create settings to your particular tastes for different types of music. It would do much more than wires or tube DACs or overblown servers.