Using an external speaker selector box would yield incorrect Audyssey processing on the 'B' speaker pair. Wrong levels, crossovers, etc. It may work sorta okay if you'd be using the front 'B' speakers solely for 2-channel use (i.e. without using the shared center and surround speakers, or subwoofer), if the needed EQ corrections are similar between the two front speaker pairs. Otherwise the results are likely to be poor.