Yes, in general a tube preamp, or tubes somewhere in the chain will reduce brightness or glare. At least that has been my experience. Something else I do that tames my speakers is I cut some felt to place around the tweeter...so it sort of looks like a bagel with nothing touching the dome itself......I can't expalin why, but that helps eliminate some of the edge in my room....I don't have an extremely expensive set up, but it is comparable to yours. Good luck. The felt makes my system less aggresive without a significant side effect.
Tube Preamps
I was wondering opinions on whether or not a tube preamp might fix or reduce my overly bright sounding system. I am currently sourced by a Rotel RCD_1520 with Rotel RB-1582 2x200 watt amp, Rotel RC-1580 preamp with B&W CM7 speakers. I know the speakers are a tad bright, but when I disconnect the Rotel amp/pre and reconnect my old NAD c317 integrated, it sound great. I like the warm sound and deep bass of the NAD. Isn't the amplifier just amplifying what it receives from the preamp? Is it possible for an amp to be bright?