I caught up with it at the original 2007 London Freewheel. Note the striking blue wheel hubs.
The machine is heavilly modified to help carry the 2kW PA system, with 52 gears and from odd forum posts it seems the hard work it goes through results in it needing a significant amount of maintenance, there is a detailed post covering the problems here.
This is version 3 of the sound system
and this was the first attempt.
Firebrox on Flickr.