Welcome! Thanks for such a great review, and welcome to the rather exclusive M50 club. Or posse. Or whatever our esteemed leader, F107plus5, is calling it this week.
He'll be along shortly.
Glad to hear that you're enjoying the 50s. I think I agree with you on the volume thing (not that I've turned up the 50s in the last few months for various reasons...)
As far as the center channel thing, if you're going to use M2s or M3s, make sure you put them far enough from the TV so they don't interfere. The VP series has much better shielding than the bookshelves, and the VP100 matches just fine with the 50s.
