Audio from PC to Ear Force PX5

I'm trying to send audio out from my computer to the transmitter for the Turtle Beach Ear Force PX5 Headset. It works perfectly with my ps3, but I can't get it from the computer.
I've got an Asus P6T Deluxe V2 Motherboard, and I'm using the optical audio out port with an optical audio cable into the optical in port on the transmitter. I've set the default audio out to digital audio. I'm not getting any sound in the headset. Any ideas?