I've had experience with all three units. I've owned an Audio Research SP-6C and now have an Audible Illusions L-1 line stage, a close relative of the AI M3A. My best friend buddy has a Counterpoint 5.1. I can tell you that the L-1 is clearly superior to the SP-6C. We're talking an early 1980's design vs. a mid-nineties design. The Counterpoint was never in my system but in listening to my friend's system I was pretty sure it was superior to the SP-6C. The Counterpoint vs. an AI M3A? Don't know for sure. The Counterpoint, another 80's design, was way ahead of its time.
