As far as I know FiiO E9 has relatively high output impedance (10ohm was it?) which makes it undesirable for 90% of headphones out there.
I can't recommend anything from personal experience but NwAvGuy's O2
is said to be one of, if not THE best headphone amplifier available for normal user. It's a do-it-yourself project but you can purchase it ready-made from various places.
Then there's always FiiO E17 ($150 or so I think) which looks promising and while (apparently) not being quite as good as O2 in the role of amplifier, it makes up by being a really good DAC on top of it.
What I'm waiting for myself is the yet-to-be-released NwAvGuy's ODA
but it might take such a long time that I'm seriously considering E17 once it gets more reviews.