If in the same room running? or just running so you have music in 2 rooms?
Either way it will be fine and safe, depending on how you have the speakers positioned in the same room will be a different story, but it is fine to even stack them or whatever, but again I assume you are doing it just to have another room with music seprate, and you don't need a niles switch as above stated really, just turn off the power amp to the speakers you don't want on if you are only wanting one pair at some point running seperate.
Either way it will be fine and safe, depending on how you have the speakers positioned in the same room will be a different story, but it is fine to even stack them or whatever, but again I assume you are doing it just to have another room with music seprate, and you don't need a niles switch as above stated really, just turn off the power amp to the speakers you don't want on if you are only wanting one pair at some point running seperate.