I think that as important as the amp pick is, so are the wires you use with it... and their set up. I use a BAT vk5i, and vk500 w/BP and the sound now, is the best I've ever had. A couple more odds and ends, and I'll be looking to do the bi amp deal. BTW I asked the question of biamping worth in another thread, and the info in it is incredible. pros & cons.. have a look at that. I am inclined to go with either BAT or VAC when I biamp the top with tubes. though I might well end up with something else entirely.
I think the vk500 w/bp is a really great amp. Especially if you're thinking of going all tubes. It's warm, quick, and possesses significant control on the JR's. Personally, were I to go with but one amp other than the 500, I'd look into getting something with 500 wpc... like maybe a McIntosh 602, or perhaps some upscale item from either PASS or KRELL... LIKE THEIR 600'S.. maybe even a pair of Krell 350's. Though I am not a fan of Krell these days. it's just athat they have enormous dynamics, if you like that sort of thing. I even thought about the CJ 350 as a suitable replacement for the 500 but stopped short figuring I'd need to swap out the pre too. As long as you veer away from an aggressive amp with the JR's, you'll be fine. Good luck.