It's an hybrid amp. I tried the headphones on the Magni and E11 when I did this review as well. The output resistance didn't really effect anything. Both the MA900 and K612 sounded better on the EF2A than the Magni anyways, so I chose to compare the headphones on the amp I owned I thought both sounded their best on.
That is true both the AKGs and the MA900s are not really effected dampening factor.
Oh I see, thanks for elaborating. If I wasn't going to buy an HE-400i I think I'd be buying a K612 right now.