A cable with HDMI at one end and RCA plugs at the other won't work. You would need an HDMI audio extractor and 5.1 digital audio to analog converter. There is no advantage to using HDMI for audio in this case. Using the 5.1 audio outputs of the PC will be as good unless you are ready to buy an AV surround sound processor for a lot of money.
A cable with HDMI at one end and RCA plugs at the other won't work. You would need an HDMI audio extractor and 5.1 digital audio to analog converter. There is no advantage to using HDMI for audio in this case. Using the 5.1 audio outputs of the PC will be as good unless you are ready to buy an AV surround sound processor for a lot of money.
^what he says. I mean right away TRS is analog, HDMI is digital, and you want to mate these together? peg into a round hole? Use your motherboard's analog output, yer done.