How do you do that without sounding negative? Because by doing that there's the risk of the general impression "we didn't agree", as you basically focused on the disagreements.

"You're totally right about X and Y. I think the only thing we disagree about is Z". People like being told they're right, and you then downplay the importance of the actual remaining disagreement. Often that lowers the stakes for people. They've already "won" since you agreed with most of what they said, so the rest becomes less important.