There is no one right answer. The requirement depends on how loud they have to play, the size and acoustics of the room, the distance you will listen to them from, and the types and contents of recordings you will be playing. AR3a used the same cabinet and woofer as AR3 (the only things they had in common) but the woofer requirements defined the overall power requirements because that is where a speaker system is usually most demanding so what was true in this regard for AR3 is true for AR3a.