If you're talking two channel audio, then you should be fine using that digital optical link.

If you're talking digital multi-channel, then you are most likely out of luck.

The way most HDTVs work, unless the multi-channel signal was generated from within the TV itself (from it's internal ATSC tuner), any multi-channel audio fro an external source is "down-converted" into 2 channel PCM, no matter how it enters the TV.

I've heard tell there are some exceptions that will do what you want, so you need to check the owners manual vewy, vewy cawfully before making a purcasing decision if this is a critical issue.