i have to say, the bh works perfectly. mine and my friends bh perform the exact same even at super low volume I've never ever experienced ANY issues.
But if your headphones hardly require any power and you can't turn up the amp past 2% and your mad because the channels are imbalanced then why are you using an amp at all??? Seems a bit of a waste and you can't even use the potential of the amplifier
I agree even on low gain with R-50 you only have minute adjustment levels.
Btw: I've tried BH with R-50 it was ok pairing to my ears, and enhanced the low end using the amps LF switch however because of the lift in top end they became a little treble happy and sibilance was also enhanced with vocals, so it might not be recommended from me. R-50 are terribly easy to drive, it's different for each individual IEM. Something like TF10 however, (also easy to drive) really benefits from the amplification.