I've been modifying my Boss DR-110 drum machine. It was the last all analogue beat box they produced. It already sounded lovely, but had little tweakability and very limited sync possibilities.
I added 6 trigger inputs for the drums. These are short circuit connections that are triggered via midi with my highly liquid MSA-P decoder.
Seeing as i had the box open I also added the tonal mods detailed on Dave Magnuson's ResonantFrequency site.
The pots and triggers for the mod are housed in a VHS cassette box, connected to the 110 via a 25pin d-type . I used every pin, plus the chassis of the connector. I plan to add the accent trigger in via the trigger out jack.
Here are some pictures. I'm editing a little video that I'll stick up as soon as.
I really like it.