I hear plenty of talk of there being "sound benefits" to be had in adding a headphone amplifier in between my device (phone/music player) and my headphones.
Unfortunately, the "why" seems to be a bit mystical and the "how" tends to remain unexplained.
There are cases where the need is obvious; with a set of Beyerdynamic cans of very high Ohmage, the circuitry in a mobile phone will be insufficient to drive it properly, and an amplifier is undoubtedly necessary.
But I'm running IEMs (and sometimes some Grado SR80s), where a high power amp isn't ludicrously necessary. I gather (and have the Fireye Minis that are supposedly a help) that some improvements in sound quality can be had in this range by using a headphone amp. To the straight questions, applicable to this sort of case...
What are the settings supposed to look like that would give me "better sound" when hooking my NuForce HEM2s to my OnePlus One with a headphone amp (let's say, FiiO E18?) in between?
How can I verify that it's working, and improving things?
What should I be listening for as verifications of improvement?