Fiio K5 is a powerful headphone amp, with a line in and line out pass through. It has a L/M/H gain with strong output and will power most headphones, even 300 ohm models, very well. It now has a low output impedance of 1 ohm, making it nicely compatible with low impedance earphones and headphones. The K5 also has a dock on top for some newer Fiio models to dock into - it will fit with the E17k, X1ii, X3ii, X5ii/X5iii and X7 models. These two units then function as one, and you can connect to a computer via the K5's usb input (without a Fiio dac docked, you the usb connection is not functional).
The K5 has a much nicer finish than the previous E9 model and features a brushed finish and excellent panel gaps/tight build.