Just gave it a try, exporting to Linux seems to work fine (so the export.cfg seems to work fine, no missing files etc. ...).
The HTML5 export doesn't run here as well, so my guess if this really broke after adding the sounds is that the fileformat used for them is not supported by browsers or the Webexport-Template ...
Maybe try converting them to .wav for effects and .ogg for music?
Btw.: nice idea for using the theme!
I think you should just go ahead and submit it anyway, the judging won't start that soon, so fixing your exports should be possible before it starts. (porting and bugfixing after deadline is allowed anyway if I remember correctly)