Determining exact power being sent to your speaker

There are technical experts here who can answer your question but for now, you should rest easy knowing that it is much more likely that you would damage your speakers from driving an underpowered amp into clipping than it would be to overpower them.

The exact power delivered to the speaker can only be measured as transient. It's power at particular moment since we're dealing with the signal and not DC. The specified power is mostly measured within the audible frequency bandwidth. The measured power is usualy done against sine wave that gradually goes from most negative to the most positive value. The gap between maximum values called Amplitude. Power measured against Amplitude is called Maximum Power. The specified power is most-likely RMS power which is product of 0.707*Maximum Power. Sound is far more complexed form of signal that less-likely can be represented by meaning of Amplitude, Maximum Power and RMS. To measure power at particular moment delivered to the load you need oscilloscope. The load is also non-linear and complex value that should also be noted. It consists of linear DC Resistance and complex Signal Reactance...

Done that somewhere in the middle of high school...

Vineman55, average music power delivered to speakers is only few percent of peak power (unless you listen to sinewaves) It is because average loudness you listen to (half of peak loudness) requires only 1/10 of peak power. In addition music has gaps. I would be more concerned with damage to tweeter caused by clipping when amplifier is too weak. Clipping produces a lot high frequency energy (harmonics) that might burn out tweeter.