I have a CODA 07x ($6.5K) preamp and a Benchmark LA4 preamp ($2.5K). I have had a lot of Bryston gear in the past but not the cubed line. The CODA 07x or the cheaper CP preamp is almost certain to be great with the 4B3. I like my LA4 better because it is not as warm but if warmth is something that is desired the LA4 will not deliver.
I should add that the Schitt Freya+ preamp that I have paired with a Benchmark AHB2 amp would likely sound similar to the 4B3 (I have heard it). This tube preamp cost $1K and has a 15-day home trial. I do like the Freya+ and AHB2 combo.