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

The Gryphon Essence is very neutral and revealing, as is the Focal's (maybe even a little bright to my ears!). As another post stated, I think your best bet is an Audio Note DAC. The Aries Cerat Kassandra is one of the best DAC's in the world, but the sound is not as "tubey" as an Audio Note. I too had a similar situation and had narrowed my choice between Audio Note and AC. I purchased the AC Helene which I should have in 6 weeks! I will utilize an Aurender N20 as a streamer.

@robert1976 

I too had been using my Roon Nucleus with Sbooster LPS as a server/streamer; in my case via Curious USB cable into a Chord Qutest.  The sound was good, certainly on par if not a smidge better than my Node 2i. Then this past February picked up a Bricasti M5 which I am now utilizing as a Roon endpoint in the same system. No comparison, a big step up from the Nucleus functioning as its own endpoint. Quieter, wider sound stage, better dynamics.  The Nucleus is functional as a server/streamer, but a quality endpoint such as the Bricasti or some such, especially in a system at your level, in my opinion will definitely reap sonic rewards. 

I’m going to zero in on something else in your system. The cabling —which is actually the cheapest component in your system, not the DAC. Your brand is a great bargain for SQ, even for systems costing much much less than yours. Their power cords and speaker cables are nice for the money and I use both. But the interconnects do not seem to perform the same…but are certainly ok for their price. Some cables can perform differently system to system, but in my system, these ICs produced unclean/noisy high frequencies and I can see how this might contribute to your issue… A high end, high resolution system deserves very clean and clear signal cables. Not to mention some absorption somewhere! Even if just at first reflection, you may see a drop in glare that you don’t even know is there.

A curse of a highly revealing system.
How long is your USB cable from Roon nucleus to DAC and what cable cable are you using?

Have you tried stock power cords on amps and DAC now that you lived with the TWL loom for a while?

My experience is that if you use a Nucleus or Nucleus+ as server & player, it tends to be mediocre.  Just as a server (which I assume is what you are doing with Mola Mola), it performs at a very high level.  The issue is the processor is too powerful to serve as a good player.  

Where I find there is significant improvement is if you introduce a master clock like what you see from Antipodes or clocking between server and DAC can be synchronized.  This happens with I2S connections or when there is a dedicated clock connection.  

My most common upgrade in servers is customers who go from a Roon Nucleus or Nucleus + to an Antipodes K50.  

You are on the right track with Aries Cerat or Lampizator.  Both are very, very good though I tend to like Aries Cerat better.  Personal taste though.  

The obvious other two options to me are the MSB Premier and the Playback Designs MPD-8 Dream DAC.  There is a slight sweetness to both with a complete lack of brightness/sibilance that is quite shocking and enjoyable.  

Theoretically, those four units should do the job and will all be a touch warmer than the Mola Mola while delivering the same of better levels of detail.