Thanks to Ray for pointing me towards this great page about Congolese group Konono N°1. They've been going 25 years and play electric thumb-pianos (properly called likembé).
They also build their own hand-carved wooden microphones with magnets from old car parts, and that thing on the left is apparently a mixer. It's definitely worth listening to this sound clip [small mp3] - the electrified likembé sound almost like 303s. Konono N°1 have an album, 'Congotronics', out now.