I had a brief look at the AK240 dedicated thread and I think the OP is best advised to ask his questions there.
He's more likely to get relevant answers to his questions there, rather than here.
A few snippets from the thread to put at ease some of the opinions here, I'll just put 2 quotes from Vinnie R. (aka Vinnie Rossi, founder of Red Wine Audio aka high end battery powered DAC, amps and miscellanea, and as I understand it owner of an AK240 along with other portable amps).
I think you can get a powerful enough amp for IEMs inside a DAP. I also believe the sound can be refined to get to the level of a high quality external amp (again, for IEMs) from a good DAP. This also eliminates the need for a cable and the plugs/jacks to connect a DAP to an external amp, which is an advantage. Whenever you can shorten the signal paths, eliminate connectors and plugs, etc. - this is a good thing IMHO.
But to drive something like Audeze LCD-3, Senn HD800, HiFiMan HE500, etc. with the authority of something like the ALO RX3 or RSA SR71B, you need more voltage swing than what the AK240 is rated for. With a 3.7V battery, the only way this is done is with DC-DC converters on board to make larger voltage rails (e.g. +/- 10V). The AK100/120 does this up to +/-3.3V I believe, and it's good, but not at the level of what something like the SR71B delivers, as it has higher voltage rails, much more capacitance on the rails to deliver higher output current, and does not need to use a DC-DC converter chips (which step up the voltage from the battery, but have much more limited output current compared to the battery). Lower impedance voltage rails gives you things like bass that hits harder and tighter and more defined, more open sounding mids, a top end with better decay, etc. Power supply implementation is HUGE because what you are feeding your headphones IS the power supply rails (modulated to mimic the input signal, with some level of distortion that is inevitable).
And even if it could be done very well for an all-in-one, I find that different headphones sound best with different amps. So having the flexibility to change amps does allow you to find one that sounds BEST with your DAP and headphones. But if you happen to find the amp inside a DAP sounds best, then you are in good luck and can travel with one box (true "portable"). And if you want that all-in-one even though it is not as good as a separate amp, then you live with the compromise.
Footnote: SR71B is a balanced portable amp from Ray Samuels Audio, rated as one of the best portable amps out there and direct competitor to the ALO RX.
Jury's still out on which is the better amp, the general consensus being the RX edges the SR71 a bit on sound quality but tends to produce some hiss with ultra-high sensitivity IEMs (but is reportedly quiet with the majority of full size headphones).
I will not continue to offer any more input on this matter since I'm completely out of my depth compared to the content of the dedicated AK240 thread.
So again, I'd recommend the OP to post his messages there.
Edited by James neutron - 3/19/14 at 1:49pm