http://usotsuki.info/fppaylod.c I got it to work. Uses the a2audioup tool mentioned by David Schmidt, plus sox to combine the output. In an additional step (since flac puked on the output of a2audioup) it sanitizes the output by running it through ffmpeg (input wav, output wav). I've tested with the ProDOS-8 payload that choked it before and it works fine. -uso.