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

Same issue, but different solution. You need to clean up the jitter which in your set up means an ethernet switch. Think SOtM sNH-10G or similar. Maybe adding optical modules from Small Green Computer (systemOptique) etc.  Again, given the budget, you should have these devices anyway, so start here first. If they do nothing, sell them. 

If I wasn’t clear, the Ethernet switch goes between the wireless access point and the DAC. 

I have two stellar dacs that fit your sonic requirements - Holo Audio Springs DAC (modified by ASi Teknology) and the Audio GD R7 DAC. The latter is stock and both check all the boxes - very natural sounding, great imaging, detail without harshness, beautiful tone colors. Just lovely sonics.

Add a grounding cable to your system and everything snaps into beautiful focus.

I second Audioguy85. I use Border Payrol DAC & really enjoy it on a good system. You can return it if you don’t like it. Sometimes you don’t have to spend big $ to get what you want.  Great small company owned & operated by Gary Dews.he’s very knowledgeable & provides excellent service! 

+1 for converting your ethernet line to optical in between the server and streamer if you haven't already. x2 converters, x2 transceivers, and an optical cable costs $100, and place a low noise power supply of your choice on the optical converter nearest the streamer. That should remove some graininess. Might push the sound in a direction you'd like.