Jed,

What's your video source type for your sports and video games? It sounds like what gonk is saying that if it's component or DVI that you could assign the 7.1 audio to that video input. If the source video is composite or S-video, couldn't you just run the video feed to the 7.1 video input and then still have your 7.1 audio feed? If you never use the 7.1 video for 7.1 video material, just piping in an alternative video source should be pretty easy.

Mind you I don't actually have a 990 so I don't know first hand whereof I speak.