You need to decode the audio on the PC/Receiver prior to sending the signal to the speakers.
I believe the X-540's are analog, so a software decoder should do the trick [360 -> SPDIF -> PC -> Decoder -> Analog -> Speakers]. There might be some lag time in the decoded signal though...
The speakers are analog. I was hoping the on board audio chip would decode the dolby digial. It works with movies thru Windows Media Player...I get DD 5.1 there no problem. What decoders are there for me to choose from?