What audio connections does your motherboard have? 1/8" analog (headphone jacks), optical or coaxial S/PDIF?
Ideally, you get a home theater setup with a receiver that has HDMI in and HDMI out. You connect the PC to the receiver and then connect the receiver to the TV. The receiver passes through the video to the TV while it handles the surround sound audio.
If you get a setup without HDMI out, but only HDMI in you can still send your PC directly to your TV, then send a separate audio cable (listed above) to the speaker system.