I would check the bridged power rating for the 3b-st on Bryston's website. I think you will see that it has a 8 ohm rating when bridge but no 4 ohm rating. There is a reason for it, email Bryston's technical support for the full spill. Your Thiels are rated at 4 ohms nominally and I think they dip below 3 ohms in places. You'd be better off biamping with the Byrston's but I think the Thiels only have one set of binding posts.
Bridging Bryston 3B-STs a few questions
I have one 3B-ST and am looking to add another 3B-St to drive my Thiel 3.6s... Has anyone had any problems bridging these amps or any negative experiences bridging any other amps that might apply to my situation? Any good results alternatively? Are there any problem with ground loops? Hum? Should I get two dedicated 20 amp lines or will one suffice? Some music (hip hop of my son's choice) can dim the lights in my house on peaks with one 3B-ST already. Nothing I listen to has done this however.