Thanks for the info. If you just want to wire for +6db full time then do this:
Right now -- and + will be connected together. Break that connection and wire the -- wire to the input ground where the - wire is attached now at the neg side of the input switch. Then connect + where the ++ wire connects now at the positive side of the input switch. This will flip you to +6 mode.
If you need a switch then pop me a mail with a ship to address and I can shoot you down a couple switches and a sketch of hook-up.