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!