Finally got an optical digital audio cable aka TOSLINK cable to connect the PS3 to my budget audio receiver, a Samsung HT-Z320 home theater. Supposedly this should give me 5.1 audio. I plugged in the cable and configured the PS3 sound settings->audio output settings. I selected optical digital as the connector and selected Dolby Digital 5.1, DTS 5.1, AAC, PCM 2.0 44.1KHz, and PCM 2.0 48KHz (selected by default, can’t be deselected) output formats.
But for some reason, some movies had no sound. On thing I noticed is that these movies all have AAC audio. I checked the specifications of the HT-Z320 and indeed it doesn’t mention AAC. Just DTS and Dolby Digital. Well, like I said, it’s a budget audio receiver. So I unselected AAC on the PS3 and tried playing the movies again. Voila! I now have audio!
What happened is that since AAC is not checked, the PS3 automatically converted the AAC data to PCM 2.0. And from PCM 2.0, the HT-Z320 can convert it to 5.1 audio via Pro Logic II. Not as good as true AAC 5.1 I’m sure. But certainly less expensive which is fine enough with me.