Audio options
You might have a couple inexpensive options for getting the Dolby or DTS signal to your receiver via a digital optical or coax cable. First, check the sound card on your PC for a digital audio output. This is the same signal that is sent over the HDMI cable. If you don't have one, you can pick up a sound card with this output for about $20 from newegg or other sites. While you are there, but the cable you need.
A second option is to check the back of your HDTV. It might have an audio passthrough output that you can connect to the receiver with a digital optical or coax cable.
A $1k+ receiver and extra HDMI cable will work, too, but I would try the $20 solution first.