I can wholeheartedly reccomend Stans Speaker Selector:-
http://www.homehifi.co.uk/S/tc-7220.htm
Although just moved mine on, had it for 2yrs to switch my main speakers between main AV amp and Quad Amp when playing Vinyl.
Really can't fault it at all and superbly well made AND it can handle bi-wire.
Chris.
(not paid or sponsored by Stan to say that!)