I have a C5. I also owned a Fiio E17. I stuck with the C5 and sold the E17. I listen to Jazz. I noticed a bass coloration and slowness in the Fiio that I didn't like very much. The C5 seems to have a more accurate and quick presentation across the spectrum. One thing I did like about the e17 was the optical in DAC function. That sped up the bass a little. It may be the sound signatures of the two companies, which has prevented me from buying a Fiio DAP as well. Based on my own unscientific, but extensive comparisons (I am a musician), and for what I want from a portable rig, JDS labs has me covered. If I get a DAP in the future I may upgrade to the C5D, but I use an Ipod Classic and etymotic er4S, and Sennheiser HD 600's. C5 is doing an excellent job. It and the er4S have really helped take away the fatigue of listening on long trips, which in turn, has allowed for more consistent study and enjoyment of music. Don't only have to be home to get it in!
