You could use an Adcom GFS3 or a Niles speaker switcher box.
http://www.ebay.com/sch/i.html?_trksid=p3984.m570.l1313.TR0.TRC0&_nkw=adcom+gfs3&_sacat=0&_from=R40
http://www.ebay.com/sch/i.html?_trksid=p3984.m570.l1313.TR0.TRC0&_nkw=adcom+gfs3&_sacat=0&_from=R40