Conan, why do you need to run audio over HDMI to your receiver and why worry about a cable to your projector?
Just run an SPDIF or Optical from your XIFI to your receiver. As long as you are using Creative Alchemy, have setup the game properly, and you have purchased the DDL/DTS Connect addon from Creative you should be golden.
Remember, if the game does not natively support Dolby Surround (most do not) you will at least have EAX as an option (which frankly is better than native Dolby for games due to specialized effects that most game developers use). With the Creative DDL addon it will then encode that 5.1 signal into a Dolby Digital stream and output it over digital. No need for HDMI.
I am using this setup today and it works flawlessly. I watch movies and play games, all over optical to my Denon 3808ci, on Vista Ultimate 64bit.