B W Nautilus 802 - How much power?

There's more to it than power in an amp, power is part of it. Its just that the speakers impedance/resistance isn't constant--it varies with frequency so any single value of the speakers resistance is a simplification (unless the speaker has an exceptionally smooth/flat impedence v. freq. response curve in which case one single value would be the whole picture). However, depending on the amp, its ability to deliver "full" power at any frequency as a product of the speakers impedence, can vary and part of the reason (or one of the reasons) why two amps of the "same wattage" can sound different driving a particular speaker--one copes with the difficult load better. Because what happens is that while the speaker may be able to provide a rather flat linear frequency response, the amp won't be able to deliver the necessary power at the given frequency (as a result of the impedence) and the result will be an audible dip, or a cumulative (that of spkr/amp) uneven frequency response. Given such a scenario, a better amp would allow the maximum linearity, in regards to frequency, of the system to be realized. I know I'm leaving stuff out so if someone knows more fill it in (cause I don't know it). But I guess that your amp should be fine with the nautilus. There is better, but I don't think that amp is going to be deficient in the power department so there shouldn't be any "straining" (unless you start clipping). If you get a better amp it would probably sound better for reasons outside of its ability to deliver power based on the speakers impedence, like lower distortion.