You find that with a volt meter - See this test is easy, next.
I "think" your looking for this:
Take the voltage, square it and divide by impedance. That would result in Peak Power in watts. You actually would want a oscilloscope on hand to know if it is clean power too
Maybe I am missing something, or am not understanding what people are asking recently but speakers do what the amps say to do. If you have 42.68V, the speakers are getting it whether they want it or not. UNLESS you have a passive crossover or such that has an overload protection circuit such as a light bulb.
95 Contour SE '01 3L 
