Timestretch of 6 mono waves (5.1)

[mp3dom]

Hi to all!
I have this problem... I have 6 mono waves that are part of a 5.1 track and I need to timestretch those waves. The problem is that if apply the timestretch to every file I have the risk that not all files are in perfect synch each other (since timestretch isn't 100% accurate). So how can I resolve this problem? Can I resolve if I convert the 6 waves to 1 single 5.1 wave and then timestretch? Is there a software that can support this? (i think Nuendo). I also would like to use the MPEX algorythm since is one of the best out there... and Nuendo supports it.
Thanks a lot!

[Skelsgard]

The problem is that if apply the timestretch to every file I have the risk that not all files are in perfect synch each other (since timestretch isn't 100% accurate).

The absolute result might not be accurate timewise speaking, but the algorithms are, so an X seconds audio will always give a Y seconds result.
Just try it. Stretch a file 10 times and the result will always be the same length.
If all your mono streams are the same length, the resulting stretching will be the same length too.

Cheers.