I have had Bryston 7bsst2, and 4bsst2 both on Spectral DMC30S preamps (really dynamic, defined powerful bottom end great highs but not entirely neutral), Threshold Preamps (powerful bottom but a bit white sounding), EMM Labs monitor controller (no comment), Prism Orpheus direct to amp (very nice), friend's BP26 (the closest to the orignal source of the bunch), and last but not least the BP25 (also very close to the source once Mike Pickett helped me sort it out). I have had no premium tube preamps on the Brystons, so have nothing to say there.
I do have a little Pas 4 from Van Alstine but it was not in the league of the other beasties. I would love to try one of his upper line preamps, or , maybe, a Prima Luna one.
Could live with any of them. Preamps get rotated to keep power caps happy. Spectral is the winter preamp (runs rather warm!).