Excellent question and one not easily answered… The easy and perhaps-most-correct answer is ‘yes’. That foolish nonanswer illustrates the difficulty in meaningfully answering the question.
For me, the first decision-tree-box question is ‘Is the speaker a 2-way with a bass/midrange* driver and a tweeter?’ If yes, chose a monoamp, as chosing a stereo amp will waste the majority of the tweeter channel’s power, because there’s very little energy contained in the three octaves of treble. The monoamp will be able to deliver all its power, properly divided by its internal crossover network, into the overall speaker, assuming the speaker can handle it. Said another way, the 300-Watt monoamp will most-likely NEVER run out of power, whereas the 140-Watt channel driving the B/MR might run out of power while it’s not using the majority of the power from its other channel.
The issue is more complicated if the answer to the first question (above) is ‘no, it’s a 3-way with bass separated from midrange and treble’. Here, the power requirements of the two sections are more equal so the above ‘answer’ doesn’t apply. I’ve done it both ways and haven’t heard a difference, but I’ve never had access to otherwise-identical amps (such as the S300 and M700). Therefore the amps I had available answered the question for me. Most recently, when I had the choice of buying one S300 or one M700 for my Revel Performa-series C208 centerchannel speaker, a 3-way with bass driven by one pair of bindingposts and MR/treble driven by another pair, I chose an M700 because Paul and company feel their monoamps sound ever-so-slightly better than the stereo equivalents. In the same vein, I recently chose two BHK (mono) 300s rather than two BHK (stereo) 250s to drive my main speakers, then biwireable Vienna Acoustic Mahlers, because, again, Paul and BHK believe that the mono 300s sound just-slightly better than the stereo 250s. This decision turned out to be highly correct, as the successors to the Mahlers are single-ampable Quad '2905s. Lucky me.
- currently and incorrectly called a mid-bass driver (and wasn’t decades ago). Boys and girls, ‘mid-bass’ is ONE octave of the range of frequencies usually described as that audible by humans. ‘Bass/midrange’ (or B/MR for short) is composed of about 7 octaves of sound–three bass octaves and four midrange octaves.