[Zag]

First a question: You describe EP as "fairly experienced but pretty loose." Is he loose with calls, or raises, too. If the former, then I put him on 245, perhaps with spades. His bet on the turn tells me that he really liked it and wants to keep MP in, and that is the only hand I can think of for which that makes sense. (Otherwise he would have bet more, or check-raised.)

You said that you think he has some kind of high hand, but what could he have? A set of aces? I doubt it. If he had a set of 9's, he would have check-raised you on the flop to make you pay for your low draw. A different set and now nut flush draw? No way. (6h 6d Ks xs? or 3s 3h Ks 2x? ick to both)

The only hand that I see makes sense is that the ace gave him a nut low, and he has something going for high -- flush or straight draw, probably both. Given this read, I would have folded the turn.

Now the river comes, and he checks. This tells me that he doesn't have the flush, and maybe your two pair is good for high. But certainly not worth a bet when they check to you.