I don't have any specific amp suggestions, other than to piggyback Rlwainwright's notion and say that I like the idea of introducing tubes into that system (and that Butler is one sweet looking beast). I'm really just writing because I love your system! I used to own the B&W 704 in Maple, and sold them to try something else, but boy I miss them. I've almost purchased another set of 704/703 just to have them and sit and stare at them, no joke. There's just something about the shape and curves of the 700 series that totally does it for me, and I wish I still owned my 704. At the time I owned them I was underpowering them, but I bet they'd sound glorious with my current gear.
I've read many comments that B&W speakers "prefer" solid state power, and lots of it, but the best sound I ever got out of a pair of 84db-sensitivity B&W PM1 I used to own came from an Audio Research VSi55, so I would not be afraid to use tubes with B&W if I were you. Especially in that particular room - you're not trying to fill a huge space there, so you need some good clean power but not truckloads of it. I bet that Butler would be all the amp you'll ever need.
Anyway, it's just funny...you have the speakers I'd still like to own, I actually do own the Rel Strata III you own (and I dig it big time), and I'm researching the Oppo 105 to possibly purchase that, so we've walked similar paths with our equipment. Your room is beautiful and so is the equipment - congrats on a great setup, I hope you enjoy it.