Preamp choice

What preamp was the suggested match for a Bryston ST 4B?
I don't think it matters that much - any good SS preamp should work - I would go for the features you need rather than try to match. I used a Rotel and then switched to an Anthem preamp with my 4B ST...I honestly can't tell if there is any difference in output, at least not enough to matter one way or the other.
i have actually had two in the past few years...first was a yba2 then eventually switched to a DeHavilland ultraverve.Both were wonderful with Bryston but i prefer the ultraverve.

You might try a tube pre. Tube pre and solid-state amp have, I've found, the best combination of warmth, accuracy, and bass power.

I have a Conrad-Johnson tube amp connected to my Audio Research 100.2 solid-state amp. Best combo I've ever had from a list of gear that's pretty long.
Tubes,had you thought about the PrimaLuna?
I owned a 4B and 7B's for nearly 10 years (upgraded to Rowland 2 years ago). I had great success with, in order:

Sonic Frontiers SFL-1
Melos SHA-Gold
Rogue 99 (non Magnum, later upgraded to Magnum)

But I think if I were in the market now, and I still had the 4B, I'd look at the Modwright 9.0. It's a great sounding preamp at a very reasonable price. You will want tubes in the preamp, and at that price level, choose a designer who is designing around reliable readily available tubes -- and not one who is running a nice but noisy tube too hot.

Good luck