I have used the FiiO - Alpen 2 E17K, with two headphones- The Beats Pro and the AKG Y50. While it performed fairly with the Beats, the real experience of the product changed with the Y50. It extended the already good frequency response of the Y50 justifying the need of a headphone amplifier. The difference was there to be heard.
The added feature of being able to change the gain level, treble and bass give the Alpen 2 a huge plus.
It is a must have for all Stereophiles!
This is one of the best (if not the best) portable headphone AMP/DAC in its price range. I have used this product for about 10 days now and i really like the wider sound stage it generates in closed back headphones like Audio Technica ATH-M50x. The small OLED display gives us the options to modify the Treble, Bass, Balance etc. which isn't possible in other AMP/DACs in this price range. The compact form factor and the brushed aluminium body are a joy to behold.
FiiO doesn't provide any assurances whether it would work with Android devices for using its DAC capabilities, but it worked flawlessly with my Xperia Z1 Compact via micro USB OTG cable.
The battery life is great and as per the values mentioned in the specs sheet. Charging time is ok ok.
Overall an excellent device for audiophiles and average music listners. If you are confused between E17k and E18, i would surely recommend you E17k due to its OLED display offering various Bass/Treble modifications.
After researching a lot of DAC/AMP I decided to go for Fiio E17k which got rave reviews from the top class audiophile sites. I was confident of playing it with PC as officially it's a sound card like amp but unsure of playing it with my android smartphone. But surprisingly with a USB otg cable I accomplished in playing it with usb audio player pro. Now I'm like flying high with my Audio Technica ATH m50x headphone. Its sound is clear-crisp and warm. What would you expect more? Now I've become a true Audiophile!