There are no footswitchable features on the Brian May recording amp...I am assuming you want to convert the high/low gain switch to a footswitch, if so forget it...it would be insanely costly plus no one is gonna want to mess with it.
As for driving anlther amp with it you plug your guitar into the input then take a cord form the "booster oiutput" jack (located right next to the gain control) and plug that into the input of your big amp.