When I play the Blu-Ray through 7.1, there is no apparent place on the blu-ray to select a sound mode so I have no idea if it is using any of the built-in Blue-ray modes or something else. Anyone have a clue on this one?
Each disc will be different, but typically the menu will have a settings or sound setup option that will let you pick an audio track (similar to DVD menus). You can also probably use an "Audio" button on the remote to scroll through the different audio tracks on the disc.
As for the 990, there is no audio processing possible with the 7.1 channel input.
When I hook-up through the optical it does not want to use any of the built in modes except perhaps DD PLIIX or DTS Neo.
When you use optical, you will get one of three things: Dolby Digital (the core DD track from Dolby Digital Plus or TrueHD), DTS (the core DTS track from DTS-HD HR/MA), or PCM stereo (downmixed from a multichannel PCM track). You can apply Pro Logic IIx or NEO:6 to any of those.