KRP, welcome. The first point is to disregard any sort of watt rating on speakers; they theoretically relate to the maximum power a speaker could handle continuously without going up in smoke, but even if accurate, wouldn't be relevant to your question.
You don't identify the receiver, but most with A and B provisions are simply a parallel connection to the front L/R channels. The result is that the impedance of the speakers on A and B(when running simultaneously)is cut in half; this may or may not be a problem, depending on the impedance of the speakers and how loudly you're playing them.
You don't detail how you'd employ the speakers connected to the rear A terminals, since usually that carries only surround sound rather than the main front channel material. You may be thinking of setting the receiver for 5-channel stereo, which would duplicate the front channels in the back channels.
Assuming that the impedance on the paralleled front A/B channels doesn't cause the receiver to shut down, what you propose seems workable.
