How to make sound less detailed with warmth?

Ohhhh....come on....CABLES ??????

It might be a good time to replace your amp.
(many to choose from.....would you like some recommendations????)

Have you ever tried room treatments ???? (it could be the answer to your problems.)

Take out your 1.5" thick butcher block cutting board from the kitchen and put it under your rotel CD player and also try one under your preamp. If your components are on MDF, I found that it sucks the life out your components when damping.

You could also change out the tubes in your sonic frontiers preamp to warm things up.

You might see about getting an estimate to fix the B&K as I spent $160 repairing my Carver amp which was only worth $140... and I regretted spending the money since I could have sold it by stating "Broken Carver" and someone would have spent 20-40 for it to use it as a project or fix it themselves.

Get some Cardas Cross or Golden Cross cables.

If listening to violins on your system is painful, you have a fatiguing system with "harsh" highs. It's a fault of your system to represent those frequencies. It's not that you have too much detail.

Tube amp, Cardas cables, room treatments.

I'm surprised that you want to loose details - thin blanket over speakers will do. It will kill both details AND brightness.

90% of people want warm and detailed sound which is very difficult to achieve. I prefare neutral detailed sound. Warm sound (stronger even harmonics) is not very good for instruments with complex overtones like piano. Piano can sound "out of tune" on very warm system. On the other hand guitar and voice sound great.