AAC 5.1 sound issue

[hrustar]

My PS3 can play 2 channel AAC files just fine, like those encoded with many of the movie trailers available from PSN. However, I recently downloaded the Across the Universe trailer in 1080p. It's encoded with 5.1 AAC audio. When I play it, i get no sound. My receiver recognizes it as Dolby Digital, but no audio comes out. When I turn off AAC in the sound preferences, and force it to send a PCM stream, I hear the audio as two channel. Anyone know why?

MY SETUP: PS3 > optical > Onkyo HTSR800 home theater sytem. Audio out on PS# is set to Optical.

[hrustar]

oops. sorry, double post.

[Sentinel]

Uncheck AAC settings on the PS3 and it should play 5.1 AAC audio.

[laprius]

just checking here is it AAC or AC3? from what I have read AAC is discrete 5.1 (needs a wire per channel) and can't be used over toslink (only over HDMI) AC3 would be recognised by your receiver as a DD signal. Did Sentinels suggestion work?

(I've been waiting for Sony to support AC3 within a .mp4 for ages now) :S