Hi I have this issue and quite frankly renders the auyda 4 useless for accordionist. I have used ketron modules from the ms40 x4 and xd3 and all allow for accordions playing manual bass.

Ketron have done nothing to resolve for Auyda 4 users and means I have two manuall reduce the volume and use the foot pedal to activate still leaving the bass sound to be bland without any effects. I emailed ketron IT as I assume many accordion players from Italy will be complaining no reply after sales with ketron is terrible