Many different approaches

Your choice of audio source is going to have to come from either the cable/satelite/Tivo/ETC box. Most boxes have an analog output (red/white) RCA jacks. This can be fed to an audio amp with speakers of your choice. If you haven't already, a low end digital stereo fits the bill. Getting audio from the PC can be fed to an auxilary input to the amp, feeding the same speakers. Some mfgrs place speakers in some funny places that do nothing to help the small speakers mounted in the HDTVs today. My first appointment for service (when it happens) will include the pairing of the case speakers through switch jacks while the case is open.