High power, low efficiency system put together in the larger of my two living areas. Very fun system to listen to, all pieces work together well nicely and are on the affordable end of this hobby.
I have a AES tube amp and for kicks I hooked it up to the pre outs of the CA 640A v2 that I use in the TV room, and it really choked the life out of the tube amp. It is shocking, because the CA integrated is a darn good integrated amp. I wonder when you go up the CA food chain that they improve the preamp section besides adding more power.
I read your post concerning your 540A being used as a preamp. I have the Cambridge Audio 640 V2 which is an excellent (even above average) integrated amp. The preamp outs work beautifully for a subwoofer..but as a preamp into a tube power amp it was not very good.
I tried the pre outs feeding an Audio Electronics (Cary Audio) Superamp Mk2 tube amp, powering 94db Polk Audio RTA-11 speakers and it was not so stunning as it was as an integrated amp. There could be a lot of reasons but as a preamp feeding a tube poweramp was not as good "in my system" as a stand alone integrated amp.
I like your anti-Sullivan treatment of your system. Instead of "form follows function" you put form first. A true minimalist. Few have the nerve to install their flat panel off-centered, or choose/place speakers for their form in a 2-channel home theater system.
What I see of your living spaces looks beautiful. I like everything about it, including your equipment. You may be able to accomplish your pre/power needs w/ beautiful minimalist PS Audio products.