How to make sound less detailed with warmth?

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.

I can't believe Ryder is the only one to mention room acoustic/setup issues. 80% of the sound you hear is the result of the interaction between the loudspeaker and the room. Before changing anything you need to consider these issues.

I can't imagine the amp is the root of your problem (ie lack of warmth/musicality). You're not likely to find an amplifier that's warmer than the B&K M200 without spending ~$1000+, and even at that price SS amps aren't likely to bring more warmth and musicality (at least I haven't found one). Tubes may be the way for you to go.

As for repairing your dead amp, have you checked all of the Fuses? I would check all of the fuses first. This includes the rail fuses inside the amp. You'll likely need to remove the driver board to check them, so if you're not comfortable with this, you can send it back to B&K or take it to a tech. Don't just visually check them, use a continuity checker. If it's just fuses, or something simple it will probably cost you $100 plus shipping (they'll do a complete checkup and bias for you while it's there). If your problem is with the output mosfets B&K probably won't be able to repair it - I don't think they're available anymore. I think the latter diagnosis will cost you ~50 plus shipping.

I think it's a coin toss as to whether you should repair or sell as is, and replace them. IMO it's worth repairing, but if I was interested in upgrading anyway, I would sell the M200s as is, and buy new amps.

One last thought - have you evaluated your room? Maybe room acoustics are to blame, at least partially.

Thank you all for your invaluable responses!
I was quite surprised by the number of posts!

I guess... the most cost effective way is to start with changing a tube then and check surroundings. My floor is carpet though. Maybe the window right next to my speaker is troublesome.

I sent back the BK m-200 to manufacturer (San Francisco to New York is quite expensive). I thought this was the easiest way to fix it.

Thank you all! I will post the update later!