Same boat... left all mine in ALAC as the Clip+ played them fine...
dBpoweramp Music Converter does an amazing job if you are in Windows.
That's still a little too bricky for me but looks nice together. It took me a while to get the Studio because it's a little fat. I said the Heir 90 because the 90 ohm impedance should be a nice fit.
Well, the c3 can power the er4s but not perfectly - at volume 40 and with shure olives it is listenable without an amp but it can't go particularly loud. Actually, I wouldn't look into impedance that much as usually there's more to it than just ohm load and output power. For instance the new Vsonic Vc02 is particularly hard to drive with the c3 and its impedance is only 16ohm - even slightly harder to drive than the er4s.
As I know C3 does not has LINE OUTPUT capability. Are you using the headphone OUTPUT as the audio source to your external amp?
In this case are you "double" amplifying your audio source?
Will it sound worse rather better because you're also amplifying the noise from the internal amp in the C3.
In addition, will it damage your headphone/earphone with "double" amplification?
The SNR for C3 is 97dB. Comparing to high end DAP, usually the SNR is beyond 100 dB.
Has anyone used the audio noise filter for the output source from C3 before line into the amp?