Hi Joerg,
The issue is that the mavlink radio status message can only send 8 channels at a time. Right now AQ only sends 2 messages, so only ch 1-16. So for channels 17 and 18 you need a 3rd message with just those two channels. You can look in aq_mavlink.c ~ line 182 where it sends the radio channels and probably figure out how to add the other 2 channels... or let me know which fw version you're working with and I can paste some code here. The QGC widget should display however many channels are being sent by the FC.
-Max