I agree in that the difference is less obvious, I use high gain mode by default because I find myself pushing the volume of both my Zune 120 and RoxClip+ to 18 and -3db respectively on max volume (purple) with my FXT90s. However, my ears believe that high-gain mode actually has less of a V curve compared to normal-gain mode. The difference was clear when I listened to MOS The Sound of Dubstep 3 last night. I found I had to use 4 increments of the EQ curve in high-gain vs 2 increments in normal-gain, to get the same sound.
Another observation is that while the bass improvement is something akin to magic ( I used a variety of crappy earphones using the RoxClip+ as a source to see what kind of improvement there is), the unit does not enhance sub-bass.
I wholeheartedly disagree with the comment about not ehancing sub-bass. Well if you mean it doesn't change sub bass at all - because even just few steps up in the contour profile on my Ultrasone Pro 750's make Phaeleh (a dubstep artist that focusses on sub bass) tracks absolutely rumble. There was sub bass presence before, and it was good, but the quantity of sub bass increases without a doubt.
Just a side note, there's a slight hiss with the Ultrasone's in high gain mode while it's charging from the USB port of my PC. It's not there in low gain mode. The ZO quickstart guide does say that if you experience any noise while charging, you can fix it by using a USB wall adapter instead of your PC to charge though.
Edited by Arnotts - 1/10/12 at 7:51pm