I'v had an AF-9 for ages, and only recently have I got it really working right, its a very tricky customer to really nail the set up of IME. Largely because the sensitivity setting is utterly key, and its this sensitivity to input level that makes it such a great filter when you finally crack it IMO.
Mind you I've never played an original Mutron III so I could be missign on some GAS here already, best bug out of this thread because that kind of GAS I really don't need in my life right now!