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

Have you tried experimenting with digital signal processing?  If not, you might want to start with what is available in Roon (including equalization and upsampling).  To take it up another level, with a correspondingly higher learning curve, take out a free trial of HQ Player. HQP integrates nicely with Roon, once you've figured out how to work the settings. 

You also might want to try measuring your room frequency response with REW. Identify the bright spots, then focus DSP (or room treatments) there.

I was on a similar journey, Naim streamer/DAC to dCS Bartok with Oppo 205 Modwright DAC as an option, then to a dCS Vivaldi Stack, and very happily to a Grimm MU1 streamer/storage/upsampler with a Lampizator Pacific DAC. You might want the GG2 over the Pacific as the GG2 is designed for a fun big sound. The Pacific seems to be showing off that like ARC's recent designs that both companies can design equipment that casts off the "old" tube sound and competes with the best of SS designs, but also includes that "tube thing" . Do not underestimate the Grimm MU1's part in my sound system. I listened to an in home demo and it took me 15 mins to decide that the Grimm was contributing in a positive way that the Vivaldi Upsampler could not match.

Lots of good ideas already posted. One is that all DACs sound alike and just get a reasonable one and that's all you need. I have found this is "sort of true" depending on the resolution of the host system and hearing of the listener. About 5 months ago for fun I ran my dCS Vivaldi DAC/upsampler/Clock (75K retail) against the DAC/streamer in my $1300 retail MiniSHD I use  it to crossover my subs and for Dirac. Long story short the $1300 multifunction DAC was WAY too close to the sound of the 75K Vivaldi. CLEARLY the Vivaldi was better, but the law of diminishing returns on DACs sets in very quickly. Many of us can't settle for good enough without not feeling good about our systems, and that is why I ended up with the Grimm/Pacific combo. I'd also like to comment on the rate of improvement of Digital and the reasonable expectation the gear will get better AND get less costly. I sold my dCS gear, bought the Grimm (new), the Lampizator used,  and after selling my dCS gear and buying the other two components I was able to put 25K back into my stereo fund and ended up with a digital system I find way more musically engaging.  There is no question that in 2013 dCS changed the trajectory for Digital sound reproduction with the Vivaldi DAC, but time and technology move forward. Further I do not sense that I gave up any resolution moving from the Vivaldi DAC to the Pacific DAC, which was my primary concern in moving to the Lampizator. The new APEX for Vivaldi dCS DAC was not out then. I expect it is more musical than the one I had. 

The last point about ideas others shared is that I used to use cables to tune my system, often for me to solve a sibilance issue. I used to do that, but I now work really hard to get components that work together in the first place, then look at cable changes to make IMPROVMENTS  in SQ, not as filters to fix problems, It's a paradigm change that costs money to make component changes and potentially buy better gear, but it has helped my system improve to my ears. This changing out of components has been made possible by Audiogon and the other websites. It's  a fantastic tool, we are in the golden age of being able to try different gear in our houses!!!! Good luck in your journey!

@robert1976 

I have a Tambaqui and in my system I would describe it as “sweet, rich, and relaxed”. Although sometimes “sweet” is not so “relaxed” when it comes to musical enjoyment!

https://www.bluejeanscable.com/articles/is-your-cat6-a-dog.htm
After reading this article from Blue Jeans Cable, I decided to try a few of their CERTIFIED Cat6e Ethernet cables. Prior to installing these my streaming was occasionally harsh and distorted. But never since. I have also found I prefer Audioquest Red River XLRs to several 4 figure cables, which also were sometimes a little non-sweet. 

Not a huge investment and heartily recommended. 

Good Luck!

Thanks for all the input guys. Apart from all the advise on equipment, I start to realise:

— When a system is highly resolving, it will expose recordings that are bright and harsh. It's actually a good thing. Over 95% of recordings sound wonderful, it's only harsh/bright with certain older (rock) recordings and at high volumes >85dB.

— My room is large and not heavily treated. Playing music loud will overload the room: at 80dB the reflections make up, say, only 15% of what reaches my ear. At 90dB that could be 30 or 40% (numbers here are for the sake of example).

Further, I don't really have side walls and thus hardly any first reflections. My right side wall is 9' / 2.7m away from the speaker (floor to ceiling windows with thick curtain). My left side wall is also 9' / 2.7m away but it's only 8' / 2.4m long, it then opens up to a large open kitchen. Rear wall is 13' / 4m behind listening position. Half of it opens up to a large study area.
Only first reflections are floor (covered by rug) and ceiling. I'm looking into absorption panels for the ceiling now.

@wokeuptobose thanks for sharing your journey, very valuable lessons.
Could you elaborate on what the Pacific does better than other DACs you've had? What do you like about it? And what are any weak points or trade-offs?