Well, it depends. If you mean the "AC3 file converted to PCM", then my point was that the original PCM file from the DVD would have more information than the PCM file extracted from the AC3 file. That being said, the center channel from the AC3 file will have less ambient noise, so it kinda depends on which is more important to you - better overall soundtrack fidelity (PCM), or better separation for the isolated sound byte (center AC3 extracted to PCM). You might do both to see which sounds better.

What I intend to do is extract the PCM file from the LD, run it through a Pro-Logic II emulation program, isolate the center dialogue, and use that for the '77 DVD version I'm planning on making.