The Pass Aleph P preamp is an excellent match with Bryston (or most amps).
Used I'd expect to pay $900 to $1500 , depending on age/remote Vs. no remote/luck.
The BAT VK-5i is also an excellent match (BAT = Balanced Audio Technology). Only hindrance here is that the VK5i uses only balanced in's/out's and you'd have to use XLR adapters for single ended rca sources (but the pre is good enough to make this worth it,...on the amp connection you'd be OK, as the Bryston takes XLR's). I'd expect a used one with remote to run $1700 to $2K(?) ,...Echo Audio in Porland OR have one on their website (a used one)
If you'd like a budget suggestion, look for a used Adcom GFP-750. This pre was designed by Nelson Pass for Adcom. It can be run passive (best) or active and is a very flexible preamp (passive/active, theatre thru put, balance on the remote two, can revearse the channels etc.) - used circa
$700
I liked the Adcom with Bryston/Martin Logan's better than Bryston's own preamps (their top one at the time, BP25 I think it's called?). Both the BAT and the Pass are even better, but cost double.
M.