...I can't hear any difference between my PC's 1150 DAC, an Asus U7 MKII or an Ol DAC.
For most people listening at their PC I would say don't bother buying a DAC.
With easy to drive headphones I would say don't bother with an amp either.
I think this might be due to personal preference, i see your point but i want to make sure something, integrated sound cards sucks.. i'm in computer science, and i can ensure you, based on 10+ years of experience that they do.. even those that are targeted for "GAMING" or "Awesome 7.1 STEREO" sucks.. mostly is some kind of bad emulated virtual 7.1 that in reality is a mere 2.0 with BAD quality.. Try any decent headphone (with decent i'm not necessarily talking about something like the Focal Elear (lul) but even something as basic as a K420 studio or something like that) and you will understand what i mean if you try to compare it with ANY decent DAC (like Fiio A3, even if now there are some better alternatives that are cheaper)