I share your frustration. I am using Audya4 with accordion, OS 5.0 and the manual bass button does not work. My bass can only be heard when the arranger is activated. The bass volume and octave parameters do not work either (while not in arranger mode). The volume levels and octaves visibly change, but there's no audible difference. Just a constant loud bass sound. I tried changing the bass midi channel from 3 to 4, but that didn't help. If anyone has any suggestions it's greatly appreciated! Thank you.