Ideal Pre Amp for Bryston 3B ST or 4B SST 2

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...

Yes you are correct Bryston pre amps are somewhat lacking.I owned Magnepan 1.6's powered at different times by 3B,4B, and 14 BSST's series amps in concert with an Audio Research LS 15 and later a 26.It was all good,great synergy between the trio.

I own the Bryston 4B-SST2 with the Bryston BP-26 preamp. I also have owned in the past:
Hafler Dh110 (made from a kit for $250 with phono)
Sony Digital 1000 pre (the first one, a chunk of embarassing crap)
Counterpoint 2000 hybrid (bought used, loved, then it broke, twice)
Adcom ??750 SS (bought new) the 'audiophile one with a blue board)
Audio Research SP-10 all tube (, used, with crummy tubes, so it was not at it's best)
Audio Research SP-15 SS with tube phono stage (bought used, still use it for the phono section)
VAC Standard tubes (bought used to use as 'high class' tube buffer, still use it just as a tube buffer for my DAC to Bryston BP-26)
And the Bryston BP-26 with the big power supply is really the most transparent of them all.
Second to it is the Audio Research SP-15, (which I found to be MUCH better than the SP-10 Heresy!, I know! but the SP-10 did have cheap tubes in it)
Then the Counterpoint, which made the most beautiful sound, though unreliable, and veiled compared to the Bryston and SP-15.
The VAC Standard is around the same 'tube' sound as the Counterpoint, and it 'fixes' my digital really well, though it has that veil....
So.. If you have really good front end stuff.. the Bryston BP-26 is really a great product. If you have ANY problems in your front end, the BP-26 is gonna show them fully.
So choose your poison. Clarity showing any warts before it,
OR, a tube or hybrid with a bit of veiling, but a smoother sound to 'hide' the faults of the front end.
That it the choice.
But when you get to the Audio Research LS-26, or the REF-3.. then you get the best of both at $4,000 to $5,500 used.. it is still pretty expensive to have your cake and eat it too.
(and all those folks who are going to post thier favorite cheaper ($2,000 new ) pre claiming it is the cat's meow.. I will be smirking at you.)