Hi Basti !
In fact, thanks to the merge function, there is a work-around for exporting a whole mixed track

!
You simply load the loop that you want to export, merge all its 4 tracks into one, save the loop to "LoopName_MixDown" for example and download this track through the Http server.
This way, you preserve the original mix of each track and have only one file to download.
I agree for iPod Touch without mic. It's probably a OS 3.0 related bug that I didn't notice because my iPod touch stay on 2.2 for backward compatibility purposes. Think I'll have to flash it to 3.1.3.
Have fun !