Zero DAC too powerful for HFI-780?

Hi,

I've been using the HFI-780 & Zero DAC combo ever since I got the Tianyun last year. It's the 09 USB edition with Opamp 627 upgrade.

My initial impressions were that the sound was richer and stronger with slightly mellowed highs. I have never bothered listening with the Ultrasone without the amp since.

Today I plugged it back straight into the iPhone and was astonished by the much clearer mids, better highs and more controlled bass. Now with the thinner sound (still rich and warm enough) the soundstage seems larger, too.

My question would be:

Is my mind just going crazy or is the opamp really overkill for such low impedance phones? I can hardly move the volume button without crankin' the volume up too high, too.

Did anybody experience something similar?

Update: I think I just noticed clipping with the Zero!

On the plus side, I'm just enjoying my all brand new HFI-780!

Could it be that it's just the DAC part of the Zero that creates more body to the sound? I know I've said "much" in my first post, but it's actually only a small difference.