Assuming that you are referring to LEFT and RIGHT balance levels. I had the same issue with my Holo Serene preamp. I wanted it in my office where I sit off centre and really need balance to make it perfect. My Benchmark LA4 (now HPA4) preamp had the analog balance control and thus worked better than the Serene in the office. However, for esthetic reasons I wanted the Serene in the office and the HPA4 in the Livingroom (no balance control needed there).
I solved this issue with the Serene in my office using the following approach:
The result of this was even better than the analog balance control of the HPA4. The Serene sounds perfect now with the settings described in my link. Nothing is compromised with the approach I used.
There are a lot of suggestions made on this thread for preamps that could not only save you money but also get you better sound. You can learn a lot about the sound of any preamp from reviews and posts in places like this. You need to first figure out what sound you are after.
Your Bryston 4B3 is supposed to be slightly warm sounding. For my tastes adding a warm-ish preamp is too mushy with the 4B3. I go with something more neutral. Maybe your Bryston BP-19 choice would be what I would choose. However, I had a Bryston BP-20 preamp years ago and it is nowhere in the class of the neutral LA4 / HPA4 or Serene preamps.