have you been able to get this to work? i also have been hoping that sentence in the manual isn't a typo, because i'd like to process some external sounds using the envelope, but haven't been successful.. looks like additional hardware is probably needed?
on the plus side, running gate out to gate in on the rear panel works fine for me at letting the audio through. it just won't trigger the envelope. you can make some very cool sounds automating the filter by turning up keyboard tracking and running a sequence, turn glide up to smooth out the transitions. still, i'd rather get that envelope working.