Well you can get the audio toggle switches off ebay, internet audio/electronics shops or radio shack. If each speaker wire goes to its individual switch before joining the main power loop then you can switch all or any of them in and out as you wish, as long as the power rating is not too much to blow any of the speakers. You may have to have a resistance on the off-side of each switch to simulate the speaker load when it's not on, so that if you go from all 6 to just one, the single speaker does not blow from having all the power instantly surging through it separately.
Does that make sense?
If you want a wiring diagram, I would suggets you post up the details on the Guitar-nuts.com forum, some very clever and knowledgeable guys there and a very helpful bunch, even though it's not really guitar-related, they are gurus at all things audi/electronic. Good luck