Would a headphone amp be an improvement over my FireBox?

[poonna]

I never have a chance to compare side-by-side with a dedicated headphone amp, but the headphone output on the PreSonus FireBox can really go louder than I would ever wanted on my new 250-Ohm Beyer DT770 Pro. I never need to turn the volume knob up more than half way on it.

I think that the FireBox was designed to be able to supply plenty of current to drive most headphones. That makes me wonder what a good clean, uncolored headphone amp would add.

Given the signal path is clean, with components selected to have tolerance enough to not produce distortion for the required amount of current, what is it that makes an expensive uncolored headphone amp (like a Grace Design's) different from a cheaper one?

I'm not including those audiophile's amps that are designed to sound pleasing here, but I don't really understand why a good headphone amp would give out more oomph or more details than, say, a good audio interface headphone output, given they are both designed to sound neutral.

Please enlighten me. You can go all technical you want. I'm ready for that!

[joshhunsaker]

get a creek audio or grace headphone amp. Mostly it is the quality, tolerance, and circuit design that makes the difference. You have all sorts of specs to look at in something like this...slew rate (the ability for the circuit to keep electro-magnet in the speaker from overshoot and problems with it's own inertia), cross-talk between the audio channels, the variation in eq responses when used with differing impedance levels of headphones, the option in many cases of stepped attenuators, harmonic distortion and intermodulation distortion, varying circuit designs (ranging from class A all the way to class F), the circuit's efficiency, chasis' ability to dissipate heat, and the obvious things like signal to noise ratio, maximum output (some really good headphone amps are rated in watts...like headroom), etc.