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

Hmmmm,

I don't know anything about streaming.

Do you have the same source in LP, CD, HiRez Stream?

Is the LP more involving than the CD?

IOW, can you isolate the Streamer from the System Sound?

Have you considered a Tube Preamp?

Robert1976 - Perhaps you might audition the DCS Vivaldi (either with or without the Master Clock and/or Upsampler).  I recently made the upgrade and found it to be free of harshness and offers tremendous detail and richness.

@robert1976 

I second the general opinion about your server. Your system is excellent, the weakest link is the Root Nucleus.

I'm a big fan of Audio Note (my system is all AudioNote). My Server/Dac was not. I did audition the AN 4.1x dac with room nucleus at my home and it was a disaster. Not impressed by any means so did not spend the money. A couple of months latter visited the local Dealer for an audition with a Inous Statement and a HiFi Rose as servers. Completely blown out. So much so that I purchase the Dac, waiting for it to be delivered with a Rose as server.

I would not change your Dac before testing  a dedicated server in your system.

Best 

@robert1976, You answered your own question in my opinion. “I used to have a Dan D'Agostino Momentum Integrated. I'd use the tone controls and simple cut treble 1 or 2 dB. I don't have that flexibility any longer.”

Sometimes the simplest solution is the best. As others have noted, recordings of rock music are often not the greatest, especially recordings of live concerts. What no one has mentioned is that the level of distortion produced by the gear used to play rock music, the amps, specialty pedals, speakers, cables, everything, are generating loads of distortion, some of it intentional. 
 

You have a wonderful, neutral and highly revealing system. Do you listen to much acoustic music at high volumes? If so, do you find the high frequencies of symphonic music, string quartets, acoustic guitar, that is, classical, jazz, folk, bluegrass, etc. equally edgy? If not, it’s the recordings.

If rock is not your sole interest and the system sounds great during most of your listening, look for a different software approach or purchase a high quality equalizer that lets you cut the treble a bit for those recordings that require it. 
 

Someone will always want to sell you a $20k something. You noted you tried Roon’s equalizer and didn’t like what it did to the rest of your music. You will likely have to adjust for the specifically annoying recordings only no matter what solution you select. Find someone who can suggest simple high quality software or hardware to reduce treble output at the frequencies where you find it annoying. Perhaps other Audiogoners can suggest some options.