The headphones I own are easily driven by the dap's I own, and using IEM's will NOT always give you better SQ. As a matter of fact it's mostly the opposite. High-end IEM's tend to be quite inefficient and often times suffer from distortion/being underpowered due to the inability of a portable to power them correctly. The use of an amp is then recommended - and most go w/the recommendation.
As for the mathematical equations your using, that's like throwing up a smokescreen to try to confuse the new members. Try using laymens terms to make it easier for the average individual to understand what your trying to express.
Either way you look at it, a Cowon, Sansa, or iPod will power most HP's quite nicely. And 600ohm can's aren't to be considered. Using something like that as an example is only trying to make the other person look like a fool - and it's actually the opposite.
I own/ed Cowon, Sansa, Samsung, iPod, Archos (the Archos has the "meh" SQ), and Zune - all but the Archos & Zune can decently power all my cans - and by decent I mean GET LOUD W/EXCELLENT SQ & BASS.