Project with wave shield Lady Ada


I am doing a project where I would like to be able to control 2 pairs of speakers. That is to say, I have arduino duemilanove, the wave shield and have attached 2 pairs of speakers and 6 switches...based on the example from the web. Now I need to make some adjustments, I need to be able to play speech in one pair while nothing in the other it possible to do that??? also, is it possible to put an amplifier between the speakers and the board...which one would be feasible?? My last question, I need to change the switches by sensors so I am not sure about the range of resistance_impedance I have to look for...does anybody know? I am not sure I have explained with precision my problem...hope so!

Thanks, Mar