I am having a dilemma. I am connecting my HDTV's speakers to my newly built HTPC's sound card using a digital audio cable, but there is no sound. I'm very inexperienced with home audio, so any help would be greatly appreciated.
My soundcard: Creative Sound Blaster Audigy RX 7.1
You are using optical? Make sure the TV has an optical in and not out as some only have out if they have HDMI. If its an optical input, just need to enable S/PDIF either through Window's Audio Playback Devices or in Creative's Audio Software.
The dilemma you're facing is since the TV doesn't have an optical in, your only choice for sound from the sound card is using the standard audio jacks which means changing the TV channel. That wont work obviously.
There are only two real options, either use the APU's sound, not 100% sure but think it does have. Or get a surround sound unit with optical in so you can use the sound card which means avoiding the TV speakers.