Problems converting an 5.1 AC3 file into a multichannel AIFF

I have an .ac3 audio file that QuickTime reports as being 5.1 (L R C LFE Ls Rs). I want to extract just the centre channel. Soundtrack Pro 3 will not import .ac3 files, so I've used QuickTime to export it to a 5.1 AIFF. I've also exported it using the "6 Discrete Channels" option.

Both resulting files open in STP showing the 6 channels and the surround panner, but there is only audio on channels 1 and 2 (the waveforms for channels 3 through 6 are flat) - essentially, I only have a stereo mix to work with. Is there any way to break it down to the individual channels so that I can get at the centre channel only?

Or is it possible that the original .ac3 is only a stereo mix, even though the metadata is saying that it's a 5.1 track? Unfortunately I don't have any 5.1 playback hardware where I'm working on this, so I can't listen to the .ac3 to see if it's actually in true multichannel surround.

 

Problem solved. I didn't know about the inconspicuous little menu in QuickTime Player 7 under "Windows>Movie Properties" that allows you to extract any individual track (or combination of tracks) from an AC-3 stream. My bad for assuming that Soundtrack Pro would automatically split an .ac3 file into its separate tracks - turns out that it just sees it as a stereo mix on tracks 1 and 2.