and there is think thing called google....
you might try it some time
do you plan to switch the signal directly from the amp outputs to different speakers? if so is it tube? or solid state?
or do you want to send one signal to different amps?
they are all basicly the same. you could do it with relays or get a big switch or digital stuff or something...
as for headphones amp there are a ton of designs
I have a few 12b4a's kicking around that i was thinking of useing for a headphones amp. there are a few schematics around for those.
if you have anything in mind i might be able to help!