How to make sound less detailed with warmth?

amp and thiel speakers are contributing to your problem. consider tubes and a different speaker. i am partial to panels, but then, you need to select a tube amp wisely.

have you considered changing the tubes in your preamp ?

Preamp: Sonic Frontier SFL-1

Patch1980, what tube are you using in the SFL-1? Try a Mullard tube.

Be sure if you are using CD as source to use only very well recorded ones as your reference for violin etc. That way you can more easily determine whether the edginess is in your equipment or the recording. See if you can borrow any other speaker that doesn't have the ear bleed reputation and see if you like the sound with your equippment. That will tell you if a speaker change would help you as much as suggested in the previous posts about Theil.

Check out a pair of Magnepan MG12QR's or 1.6QR's. Read the latest Absolute sound about them. The B&K's are not bright amps at all. If you have a competent repair station there have them repair it. But call B&K and they will give you some idea of how much. Of course they will be able to turn it around more quickly too I'm sure. The mosfets are out there but can be hard to get.

I have a friend that had his B&K 140 monoblocks repaired last month and the output on one channel was gone because of a resistor that went belly up.

You may want to change the tubes in your SF SFL1 preamp to a warmer tube too.

I actually got a Scott Nixon Tube DAC and I'm using it instead of the built in DAC on my DVD/CD player and it has taken all the edge off my digital playback system period. I was using a Pioneer DVD 563 but I have an Oppo 980H Now. Wonderful with the DAC. No edge or brightness. I changed the digital cable between my dac and DVD player too to Vampire wire.

Last with the cables try some very good quality copper cables an wire instead of silver cables.

The Scott Nixon DAC may be the best solution after getting the B&K's fixed. Then Try some Maggies. They may surprise you.

The Thiels can be tamed but you have to play with them. It does take time. TUBES for the warmth factor.

Carpet floor. Absorption panels at both side walls. If that's not enough, stack them all at the back wall. Will kill highs, detail and dynamics. Place them at the front wall as well and you have a acoustically dead room.

The others have given good suggestions.