I just got a set of the pro's delivered yesterday and have to commend you on the build quality. These are hands down one of the best quality metal enclosures I've ever seen, and are insanely comfortable.
I find them really lacking in the lower end though with a very week sub bass. Burning in now to see if it makes any difference, but I'd love to see a new model with a big boost in the bottom end for us bass heads, drum and bass and edm fans as I'm in love with everything else about these phones.
They do sound a little better hooked up to your e10k amp but still need a sprinkling more sub bass rumble
We've had the f9, weve now got the f9 Pro, now we just need the f9 Low