[Jack Bonnett] “The Audio track mixer is set to send A1, A2, A3 and A4 (all centred) to 1+2 and A5,A6,A7 to 3+4.”
OK, thanks for the explanation. Please post a screen capture of your AME audio export settings.
If there isn’t a simple solution in AME you could create a new sequence in Premiere Pro and export with 2-channel audio.