Actually, I have used a Sony MDR-V6/-7506 straight out of a laptop's soundcard -- it sounded a little bright and rough around the edges, but not that much different than it would out of an amp. (I.E. I don't think it scales much at all -- the roughness would go away with a different source, but that's about it.)
Also, I've used a pair of Etymotic ER-6i's directly out of a Creative Labs Nomad Jukebox 3, and it sounded surprisingly good for portable audio -- I've stated before that if you're not going to use an amp, then that's the way to go for entry level IEM's and portable audio.
So I guess I was arguing with the general statement, since that's the direction you took this debate, and not specifically with the Denons, whose scaling I have little experience with.