The iPod will not be able to drive many headphones. It does not drive my 250-ohm DT880s well at all. I have read that the DAC on the iPod is good, relatively speaking. So I imaging it is good with earphones. I find the C5D to be a good performer, but a tad lower in SQ compared to the O2/ODAC for instance.
Thanks for the quick reply!! I believe the phrasing of my question wasn't clear enough. I meant the iPod's line-out to a C5 compared to the C5D as a whole. I'm looking for another external amp for the iPod (right now it's stuck to a Fiio E11) as the Duet is rather large and the onboard amp of the iPod Video is recognized to be its bottleneck. If the C5D amp/DAC combo is better than the iPod/C5 combo, I'd get the C5D and just use an Apple CCK with my phone.