how to prevent PS3 from outputting MP3/WAV in PCM 5.1 channels?

[Kryptron]

So what's the problem? You play music in stereo and it outputs the sound in two channels. That sounds like its working properly to me. If you're wanting surround sound from a stereo source set your reciever to ProLogic. That's all I can gather to tell you from the way I read your post. Hope this is helpful.

I don't think he can. The receiver doesn't give me any mode options when playing music from the ps3's hard drive. On my ps3 the only options when playing music from the hard drive are Direct or Multi channel. I get sound from the front L/R and sub no rears, thought for music i don't really care for surround.