Bryston amps Bridged3B's or 4B?

I recommend you post the same question over on the Bryston Owners circle on AudioCircle. There's a lot of expert Bryston knowledge there--and probably someone who's tried just what you're asking about.

Are your speakers bi-wireable?

If so, you could go the vertical bi-amping route, without having to bridge (and lose power into lower ohms as Bob R. suggests).

Drive the tweeters or tweeter/mids with the 3B, and get another 3B or even better a 4B for the woofers.

If you search the Vandersteen FAQ page you'll find quite a lot on bi-amping. RV explains that when an amp is only connected to the tweeter/mid terminal, it "sees" the caps protecting the speakers but not the resistive load provided by the woofer. This situation can in turn cause the amp--particularly ss amps--to oscillate wildly, which can cause speaker damage (not covered under warranty).

RV seems to like monoblocks snuggled close up to each speaker. Still, I'm not quite sure about the need for more power, as RV repeatedly makes mention of 100W or at most 200W amps being more than sufficient, and Brystons aren't exactly current-impaired...