The C4 only has digital output. So no line out means you can't connect to a normal analogue amplifier. You could send the output to a DAC and then into an amplifier but then you're not using much of the splendid C4 circuitry. I suppose this player was designed to be so good as to not require external headphone amps which often improve upon the built in amp. Edited by Sefelt103 - 11/11/12 at 12:07pm
One of the great features of the c4 is the amplifier.
At home I use a Sugden headphone amplifier. Still the Colorfly is a good match.
I tryed headphones from Ultrasone, grado and sennheiser on the Colorfly.
No problems handling etheir one of them.