I agree, the sound and dynamics change to the better when volume is above 70 or 75%. It's not from good to great, but from bad to..well still disappointing. See http://www.6moons.com/audioreviews/nuforce17/1.html. Reviewer, Srajan Ebaen, elaborates pretty much what I am experiencing. Sound won't come out. Flat as a pancake.
I don't think the nuforce DDA-100 treats input in a very neutral way. On the contrary, I hear inability to deliver the power and accuracy needed for proper reproduction of bass and drums (even just acoustic bas and drums - no metal, speed pedaling). Treble is metallic, not neutral. Trumpets, saxes, guitars, cymbals and even vocals become ear-tiring. My Dali Ikon 2 normally handles the high frequencies very well and I have had access to high-end gear. I know how my music should ideally sound.
Like I don't blame a tiger for being a tiger and for eating a man, I don't really blame the nuforce-DDA 100 for sounding like a digital amp because thats all it is. I just think the reviews and marketing is misleading. I suspect, like aformentioned review, that my nuforce is less sophisticated than the models that was origianinally put to the test. That would explain a lot and of course raise some serious questions to the nuforce people.