The 990's USB input supports PCM only, so you couldn't pass Dolby Digital or DTS bitstreams through it. You'll need the TOSLINK connection for those formats, which means figuring out what settings or software is needed to feed a native bitstream from DVD sources and to generate PCM stereo for other sources. I'm not sure what software might be required for that, but there are some good HTPC forums around that could probably give you a wider array of answers (there aren't many HTPC users around here, I'm afraid). AVS might be a good place to start.