did you hook up the preamp and amp without the trigger? You have to turm the amp on first to avoid a popping noise. If you did, and the units operates, your problem is simply that you are using a stereo connector instead of a mono connector for the trigger. (your adcom 750 is probably fine)

As for the remote for the 990 . When i first started using the unit i was careless where i placed my fingers and often at first pushed buttons by accident. I still do sometimes, when i pick the remote up. Sometimes, this sets the clicker so it will not change inputs. Pushing the button marked tuner in the upper right of the unit, just below the one marked tv and THEN your input button located along the bottom three rows at the bottom of the clicker changes your input. (I think it resets theclicker to operate the preamp controls instead of a particular input) Hope this helps martialovid