This may seem like a weird guess but here's my reasoning:
A) Since me & AngelBack got them all wrong, none of the answers can be what we said, so A can't be MP. Since Mladen & Robo both got one right, it has to be one of the ones they said the same, so they either got B or C right, so they got A wrong. So A also can't be KM or JP. This leaves only CD or JM, we'll come back to this.
B) Since I got one right on the second guess & I guess A as KM. That means I also got one of either B or C right, which means that Mladen & Robo got B or C right & I got the one right that they got wrong. For B, they said CD while I said MP, so it has to be one of those. Again, we'll come back to this.
C) Same logic again, they guessed MP while I guessed JP, so it's one of those. If Robo/Mladen got C correct in saying it was MP, then my answer as MP for B would have to be correct. This can't be right because every quote is from a different band member, so C has to be JP.
B) So then if I only got one right on my second guess, that means I got A & B wrong, meaning B also can't be MP, so B has to then be CD.
A) So then if B is CD, A can't be CD either because again, every quote was from a different person. So then by process of elimination, A has to be JM.
Therefore:
A. John Myung
B. Charlie Dominici
C. John Petrucci
(Edit: This also fits Renzo getting 2/3)
(Edit 2: Shortened the explanation slightly to make it more readable)