Just got my BDP-83 this week and all hooked up and the same problem with the optical and changing tracks. I also just called Oppo and they said it was an issue with the compatibility of the BDP83 and the 990 and they are working on it with Outlaw.
I do have the 7.1 Analogs connected but when listening to regular CD's I really enjoy the 7Ch Stereo to fill the room.
Hopefully they will have an update for it soon.