I've been working on some PMODs for interfacing with audio devices. I've put the kicad files on github.
https://github.com/mdovey/pmod_optical is a PMOD for interfacing with digital optical audio using either the SPDIF or ADAT protocols (although could be used for any data over a suitable fibre optic cable with a JIS F05 connector; however the components are only rated up to 16Mbps)
https://github.com/mdovey/pmod_midi is a daughter board/shield to allow CME's Widi Core MIDI over Bluetooth module to be connected via PMOD.
I'm a newbie when it comes to this sort of electronics, so apologies in advance if there are only glaring errors!
Matthew