Off & on since I've owned the 990 in the course of watching a DVD movie the sound suddenly "goes away". When it happens the remote usually becomes inoperative, and about 75% of the time so do the controls on the face of the 990. Turning the 990 off, counting to ten, then turning it back on will usually bring the audio back, or if the 990 faceplate controls are still operative toggling the surround type will also bring it back. It happens usually 3 or 4 times in the course of one movie, usually playing in DD 5.1 with no consistant time between outtages or any cause or commonality that I can determine. It doesn't happen with every DVD I play, but one that consistantly has the problem is "Stargate".
I'm using the Oppo 971 DVD, connected with the DVI & Toslink connectors, set to "raw" output and currently set to 96K rate (I think-). Occasionally it also happens when using my older Sony DVD (outputting PCM) while playing a CD, also connected with the Toslink.
I haven't done the firmware update yet..
Any thoughts or fixes?

I'd recommend installing the firmware, but I'd also give Outlaw's customer service a call - that's not something I've heard of other 990 owners experiencing, and it sounds pretty odd to me.

With Steve's help I believe that I have the answer to my "sound drop-out" issue- I have been tweeking my system while I watch the movie, and have left the OSD "open" on the monitor- Steve pointed out that leaving the OSD up while watching can cause the exact symptom I've been getting- I'll set the OSD to time-out at 20 seconds or so, and hopefully that will take care of it-
Again, thanks to Gonk and to Steve for thier help and input!