What Haylo said is correct, you will have no problems running the cables like you planned. There should be a setup option in your Hd DVD player to specify how you are connecting your audio. A cable card is just like having a cable box in your TV so the same setup rules would apply.
I take it you do not have an HDMI receiver to take adavantage of the sound formats that HD DVD's have to offer.

A computer once beat me at chess, but it was no match for me at kick boxing.