Thanks, Bob. You are a true team-player.
It was a fascinating exercise. As others have mentioned, it was far more difficult than I anticipated, probably because I found very little difference between the two speakers relative to either midrange clarity or bass extension.
The two primary differences that stood out for me were the quality and smoothness of the treble, and the spaciousness of the imaging.
I found that speaker B (later identified as the M3) was quite a bit "bigger" on most recordings
As to the treble response, speaker A seemed overly "hard" to me on a number of selections, to the point of being strident or unpleasant on hot recordings. Speaker B was far more forgiving, although perhaps slightly less "airy" sometimes.
Some strengths and weaknesses were only apparent on some tracks.
Overall, I preferred speaker B by a narrow margin, but regardless of price
It really was an extraordinary opportunity to participate in a completely blind listening session like this.
I'm sure Ian greatly appreciated the chance to collect valid - and validating - data from an international panel of experts