eac3to is an excellent program, especially good at converting PAL audio to/from NTSC with no noticeable quality drop.

At the end of the day the best tools available are your ears and your judgment. If you hear no difference and you're satisfied then its probably good enough.

That said, I can confirm that Darth Mallwalker's method works perfectly and maintains synchronisation with the video at 23.976fps (no surprise there, of course!). I'm currently watching ESB having resampled the audio and adjusted the sample playback rate and everything is in sync and probably as pure as its going to get, including the volume adjustment; technically it could have been avoided but the source reels really are just too loud at their standard levels.