thanks for the idea. tried to disconnect all other usb devices, but it didn’t help. actually, i think the usb transmission itself is ok (mpk works fine with other software and even with plugin sliders in renoise). it must be some problem in how renoise handles some particular mappings (volume faders).
as for drivers: mpk is a driver-less instrument, ie. it is a class compliant usb device that uses default system usb drivers.
if i find enough time, i will try it with duplex yet - probably i can try to modify akai lpd support Duplex Device: Akai Lpd8 , although im generally very bad at coding…