I have made my own aepp that is still work in progress but I might as well share it:
<?xml version="1.0" encoding="UTF-8"?>
Make a mp3 copy using Lame
As you can see it starts C:\Lame\lamebat.cmd after finishing the mixdown.
In the lamebat.cmd file I have the following:
C:\Lame\Lame.exe -b 320 %1
C:\Lame\flac.exe -8 %1
C:\Lame\qtaacenc.exe --cbr 320 %1 %1.m4a
After a mixdown it uses the finished Wav and makes a MP3, FLAC and M4A (AAC) file in the same path as the Wav file.
The %1 is a VAR that the .cmd script uses and is the same as $PATH (the path and filename of the mixdown file)
So it really requires the executable to be able to take arguments, unless you really want to go deep.
A dropbox aepp xml should be easy, you really just need to copy the mixdown file to the dropbox folder.
Hope I didn’t confuse You, being on PC and not knowing OSX makes it difficult