I can't get them to talk to eachother! I have three other midi pedals hooked up to the mastermind and they work fine, but when I added the fourth, I can't get the Preamp to receive messages from the mastermind. To set the Preamp's midi channel, I have to hold down some buttons til the display flashes, then send it a message from the mastermind, and whatever Midi channel I send it on is what the Preamp sets its Midi channel to. But it just never gets that message. Any clues?