I'm saying that I can't tell the difference in sound quality on the iPad2 with my HE400 plugged directly into it versus iPad2 -> O2 -> HE400 at the same volume with ALAC files. I think the iPad2 can get plenty of volume for the HE400. I haven't really compared an iPad2 with the HE400 directly connected to it versus the O2/ODAC with the HE400 yet. Sorry for any ambiguity.
Oh I see. It makes sense that you would not hear a difference, as you are still using the iPad's DAC and amplification - the O2 is just replicating that output with the benefit of higher power.
My Cell Phone sounds just as crappy with or without the O2 plugged in to it. A better way to 'upgrade' your listening experience would be to try a different source with the O2.