Only outputting 2 channel

[Rantox]

Hi,
I have newly installed PMS and am using it to connect my mac mini to my PS3 to play movies. I have built up a large number of movies and the majority of them have 2 audio tracks encoded , an AAC(Core) 2 channel and an AC3 5.1.
It seems my PS3 is only reading the AAC. Is there any way to tell it to ignore the core audio and read the AC3 instead.
I have 1 movie that i have encoded with just 1 audio track, an AC3 5.1 and this streams through fine and plays 5.1 from the PS3.

Kev