Actually, if the audio source you want to listen to is really just an audio source (CD, Aux, Tape, or the tuner), you can switch from a video source to that audio source and the 990 will continue to pass the video from the previously-used video source. I do it all the time with the cable TV and a CD or my Roku SoundBridge. Drives the wife nuts because the picture and sound don't match up. I've also used it with CD's played from a DVD player by switching to the DVD input then to the CD input so I can get the player's on-screen display while using the CD input's stereo settings...
If you are only using the projector with the Denon DVD player, that leaves the two HDMI sources and the one composite source (Wii) to contend with. Do you want to watch DVD's on the Toshiba using the Denon? If not, you can run the video straight from the Denon to the projector.