Re-Timing AC3 audio

[kozikowski]

<<<I am working on a UK PAL 25 fps release, which is derived from a Digital Beta master tape (but sadly the master tape does not include the newly created 5.1 Dolby Digital EX and 6.1 DTS mixes>>>

It wouldn't. DigiBeta only supports two AES/EBU streams (four audio channels total).
DigiBeta also doesn't support 23.976.

You didn't say the magic words "I'm working from a PAL DigiBeta..."

Were you able to blow the Dolby Digital out to the six tracks and mount them in Audacity OK? Without doing anything else to it, were you able to generate a new Dolby Digital stream? If you can't do that, anything we do in the middle doesn't mean anything.

Koz