A hdmi distribution amp will enable you to distribute the video card output to mutliple displays.
You may want to set the video card to a "common resolution" for exsample 1024x768 is a pretty generic resolution accepted by all displays.
If that does not work, then look at adding a HDMI...
You can use an external HDMI switch with optical audio conversion features. For example, you can connect the Xbox 360 to the HDMI switch using HDMI and connect the Optical output from the switch to the AV receiver for Surround sound. For example, this HDMI switch has several 4 HDMI inputs...
Welcome to HD world. Here is what I found. If it is a cheap AVR then it is likely just a HDMI switching Audio receiver. This simply allows you connect multip HDMI sources thru your AVR to the HDTV. A tru HDMI processing receiver like the Yamaha 663 ( which I have) is excellent will have...