IMHO there is no "ideal" preamp for Bryston amps.
Now I have had a few tube preamps (both balanced and single ended - Hovland, Rogue, Lamm) that have worked well with Bryston amps but would suggest that Audio Research products could get you what you are looking for (given your desire for balanced connections). I currently own an ARC LS-26 that does a great job with my Bryston amps.
An alternate choice would be to buy a used BP-26 with the new full size power supply and try that out. I can personally attest that I have found that to be a better preamp set-up than a BP-20 when matched up to a Bryston amp.
You might want to make the decision on the amp first as the SST2 series is quite different that the ST version and in the end could play a significant part in which preamp you ultimately end up with...
Now I have had a few tube preamps (both balanced and single ended - Hovland, Rogue, Lamm) that have worked well with Bryston amps but would suggest that Audio Research products could get you what you are looking for (given your desire for balanced connections). I currently own an ARC LS-26 that does a great job with my Bryston amps.
An alternate choice would be to buy a used BP-26 with the new full size power supply and try that out. I can personally attest that I have found that to be a better preamp set-up than a BP-20 when matched up to a Bryston amp.
You might want to make the decision on the amp first as the SST2 series is quite different that the ST version and in the end could play a significant part in which preamp you ultimately end up with...