Extrapolated volition means what we would want if we were wiser, more virtuous, etc. Coherent extrapolated volition is a way of expanding the concept across many people -- what the group would want, collectively, if its members were wiser, more virtuous, etc.

So if the mirror shows CEV, and there are two people looking into it, you'd expect it to present images that satisfy the two people's collective CEV.

What would that look like? Well, Harry and Voldemort's collective goal structure is obviously pretty different, but they both believe that immortality is desirable and that death is an enemy to be overcome. Both of them believe (correctly?) that the Philosopher's Stone is necessary to achieve immortality. So both of them want Harry's plan to work to retrieve the Stone.

What else? Voldemort wants to defeat Dumbledore in a battle of wits, but he doesn't want to kill Dumbledore (i.e. the bit about preferring chess to solitaire). He also enjoys showing off his intelligence. He has no interest in helping other people, or really anything that involves kindness to other people.

Harry wants to defeat death for everyone. He wants to bring Hermione back from the dead.

What does all of this have in common? How could the mirror concoct a fantasy that fulfills only the parts of these goal structures that overlap, and none of the parts that don't?

How about this? The mirror isn't fooled at all by Voldemort's confundus charm; the reason that it shows Voldemort his own conception of Dumbledore's family (and does not show it to Harry) is that that is what success looks like for Harry's plan to retrieve the Stone, which they both want.

It also shows Dumbledore becoming trapped in time. That satisfies Voldemort's extrapolated volition because Voldemort gets to defeat Dumbledore decisively, in a battle of wits, without killing him, while showing off his intellect to Harry. And it satisfies Harry's extrapolated volition because Harry believes that Dumbledore is pro-death, and is likely to obstruct Harry's plans to resurrect Hermione and defeat death for everyone -- so it gets him out of the way, without injuring him, until after those plans can come to fruition.

But presumably all of that could be an illusion, except for the stone in Voldemort's hands.

I have no idea, though, why Voldemort was trapped in the field of the mirror when Dumbledore appeared. That is the biggest strike against this theory that I can think of.