Ian,

I just tried your pre-mix by merging all tracks to a single stereo audio track...then exported that SINGLE track to a wav file and it is STEREO ! ... but this is only a 'work-around' .. I'd still like to know why the Merge to stereo file does not work..

Here's the stereo version of the mono track above:

http://soundcloud.com/mitchc-1/steelin-home-c6-1