Elberoth,
You are obviously taking a very careful and thoughtful approach in the construction of your room and its design. It looks beautiful and I'm sure it will sound wonderful.
No offence, but I wonder if you should hold off changing your amps. I know some on Audiogon change their equipment as frequent as I change underwear ... but I know you are more thoughtful than that. Yet, you have recently been posting about a number of SET amps, since you purchased your Lamm M1.2's.
I would wait until the room is complete and you have a chance to listen for a few months. Perhaps, relooking at the preamp may accomplish what you are looking for in the presentation and midrange magic, without second guessing your amp.
Regards,
Lawrence