I apologise in advance, as I can't remember whether this is GPO or not. It's a quirky piece, and not entirely satisfactory - the reason for that is that a student of mine (a very weak student) wrote the rather naive string part for the first 7 bars or so. His entire composition was 4 repeats of those 7 bars, and he was very proud of it - so whilst he allowed me to convince him that it completely lacked a foreground, I wasn't allowed to touch the chords, which is why it hangs around each for too long.
In the space of an hour's lesson we wrote the xylophone solo over his few bars, and then I showed him how some of the ideas could be re-used and developed. Finally I brought home the MIDI file and, I think, rendered it with GPO (we had been working on the built in sounds of a Soundblaster card) - but there's a slim chance it was the Siedlaczek orchestra. I can't tell, since the files are long gone, and I can't even remember how long ago this was, in order to work out my setup at the time. I'm about 80% sure it's GPO though, so I decided to go ahead and post it.