I put this post in a separate thread since it is a different modification by a different person(s).
The modification by AnalogueSolutions is to add another audio out so that the "upper" and "lower" sounds come out of two separate audio outs. I havent tried this mod personally, but it sound interesting enough that i might order it. I asked them whether the "Balance" knob on the JP-6 will affect the volume sent to each audio out, but they said they couldnt remember. Either way, the ability to send the upper and lower sounds to two channels on your mixer and apply different Fx, Eq, etc.. sounds (to me) like it might be worth the modifictaion.
Their website is: http://www.users.globalnet.co.uk/~concuss/mods.htm