[LAU] Soundcraft MTK22 + jack: first 16 channels silent

I have an old problem (also posted in august) that I'l like some ideas how to solve. I have two computers, a laptop and a desktop box running identical setups: Debian stretch with 4.12.0-14.3-liquorix-686-pae kernel and jack version 1.9.10. On the laptop my mtk22 works perfectly, on the box the first 16 channels are silent. The laptop has two usb ports, one is blue (usb3 I guess) and one not blue (usb2 I guess), the mtk22 works with all 24 channels on both ports. The box has several usb ports, some build-in (usb2) and an usb3 PCI card I added. On all usb ports the first 16 channels of the mtk22 are silent. I'm led to believe that the problem is a software/configuration problem on the box, due to: 1) the box worked perfectly with the mtk22 when I ran debian 8 (jessie) 2) the box doesn't work even with the build in usb ports I'm suspecting "something" might be grabbing the first 16 channels of the mtk22 somehow, tried disabling pulseaudio (sudo chmod -x usr/bin/pulseaudio and rebooting), still doesn't work. Obviously I tried with several usb cables, the results are the same: the laptop works, the box doesn't. Any ideas how to approach this, pointers, things to check/try out would be greatly appreciated! I'm pretty lost... Thanks in advance! -- Atte http://atte.dk http://a773.dk