Kent, I think you may not hear much regarding your specific question about the Whisper and McIntosh 501 amps; there would be precious few people who have that specific arrangement. But one never knows unless asking...
I have found that it is not necessary to have tremendously powerful amps to drive the DSW. I have used one stereo Cambridge Audio Azur 840W on the bass and two Pathos Classic One MkIII tube hybrid integrateds in Stereo mode on the M/T with excellent results. Neither of these amps are "monsters" in terms of power; in fact the Pathos amps are 70wpc powering the M/T! I think the correct word for my reaction to the depth and power of the bass was "stunned". I expected nowhere near the amount of subwoofer-like power and depth from the single Azur amp driving the bass. I'm eager to at some point use the other 840W I have and run them Mono on the bass. THAT would be quite interesting.
Because one can adjust the gain through the processor and the speaker is about 95 dB sensitivity, one can use moderately powered amps and get great results. McIntosh 1.2KW Monos would be serious overkill (But, I like overkill!), much more than enough. Typically a company's amps improve sonically with additional cost and power, so I certainly wouldn't discourage a better offering. It is not necessary, however, to drive the speaker well. If a person has the means to secure the higher end amp they should because the sound quality will be improved. It's not just a question of power; with the Whisper the power issue is less critical than with many other speakers, but the quality of the amp will be clearly revealed.
My experience is that the brand of the amp - its particular voicing - will play into the equation of seeking one's ultimate sound as much as the power of the amp. So, do not assume that mega-power will solve all. Seek an amp which sounds lovely to your ears and as long as it has moderate power the Whisper can make it work (remember, you've got gain adjustment with the processor). Is it conceivable that you may like the sonic attributes of a less powerful amp to drive the Whisper versus a more powerful amp of a different brand? Yes; there is some experimentation involved unless one simply wants to pick a favorite and use the processor (if so desired) to optimize it.
