The Fiio E12A Mont Blanc portable headphone amplifier is a great amp for IEM's and earbuds. The sound signature is slightly on the warm side, and presents a much fuller sound and wider soundstage than normal when using it with my AK Jr player. I particularly love the bass boost as it adds extremely clean sub-bass which doesn't bleed into mids, and is still acceptable in quantity (I believe it's +5 dB or so). The sound differences are not drastic, but they are noticeable if you A-B test the AK Jr and the E12A. I love the sensation that the sound has become fuller. For the interconnector I used the Fiio L16 3.5 mm to 3.5 mm silver interconnector.
Design-wise it looks really good, especially with the AK Jr.
Overall a great amp, and especially useful for IEM's and earbuds in particular (for which it is made for). I use the earbuds I have on low gain, but that's because they are all low impedance. I will test a 300 Ohm earbud soon on it and see how it holds up.