It would still be rough, since most speakers are impedence variable with frequency, and amps are supposed to be voltage sources (mostly). So you'd have to know the exact impedence the speaker would display to the specific signal.....

Plus, I bet if you sent a 99 watt 17kHz sine wave into them you'd smoke the tweeter in no time.

The power ratings on speakers are pretty much meaningless - what I'd like to see would be a set of curves, the decibels output at thermal limit vs. frequency and the decibels output at physical limit vs. frequency. Maybe a 'music duty cycle' (1 second on, 4 off or???) decibels output at thermal limit vs. frequency would be good too.

But that would be too much truth in advertizing I bet.