The difference between the speakers direct from PC vs through the DAC wasn't nearly as profound as with the headphones. I think for any amount of money I'd be pissed with these headphones if I were running it only through the PC. They were completely lifeless and didn't get nearly loud enough. At the 12 O'clock position on the DAC the volume was already significantly louder than max through the PC. There is no point in spending time on specifics, everything about running the headphones through the DAC was better.
As for the speakers I really can't put a finger on one thing either, it was like jumping from 128 to 320kbps MP3's. To me it was all the same sound, just sharper and had better detail. I think eventually I will play around with rolling opamps to try and bring out a bit more bass but that may just be limited from the 5 1/4" speakers as I didn't notice much difference in that department.
I wish I could give a more thorough review but this is my first dac/amp and my hearing is trained as well as most of the other people reviewing. Could I tell there was a difference? Absolutely. I'd say it is a must have upgrade for anyone that sticks to mostly headphones. People running only speakers and are on a tighter budget can definitely go without. As for non budget minded speaker folks, also worth the upgrade.
On a side note, the headphones will pick up interference from cellphones so keep them separated.
