oneneo

Bought the XS 708b from a friend. Thinking of getting a new pair of headphone to go with it. Can you recommend which HP is best for it? What is the optimal impedance headphone that works best ? Thinking along the lines of DT880, DT990, K701, MS-2 and the likes. I know it's silly. I should get the phones first then find the best amp. But then since I already got the amp... Appreciate any comments.