I just picked up a used G-K 400RB off eBay, and have a question that's not addressed at G-K's site or anywhere else I've looked. (The 400RB manual on G-K's site is a bit thin on information.) This is the version that has a jack next to the boost knob. What switchbox will work with this, and what will it control? I've heard that it will switch boost on and off only, but I've also heard it will control boost and will also switch the effects loop on and off. Who has a 400RB that can help?