With USB, most DACs are limited to 24-bit 96 khz which is DVD quality and then some. The coax can take you to 24-bit 196 khz, but this doesn't matter if you aren't listening to Blu-Rays. If you are just jamming out to your headphones, your music is most likely from a 16-bit, 44.1 khz source anyway, so the added resolution from digital connections is not necessarily a big plus.
so if i just insert my headphone (any) into the S/PDIF headphone jack it will give me 16-bit, 44.1khz most likely on my laptop.
what about if i insert it with an Optical line from a Dac? e.g. DAC->Optical line->Laptop?