Good to get that info firsthand - I suspect that iDevices might work better with the DFB at low volume levels. I had the opposite experience with my Lenovo tablet yesterday - sleep deprived and I really wanted something mellow with my Senn CX5.00G but the best I could manage was the level I normally listen at in a quiet room and that was too loud on a lot of my music. You know something isn't right when you have to go back to the headphone out on your device and put your DAC in a drawer, but I completely get that AQ had to make the DFB work across a huge range of devices and the whole ballgame changes when I get on a bus and the 'max recommended volume' from the HO is too wimpy to compete with the noise around me. Perfect world, I would love to have the DFB connected to the back of a CUBOX or similar small form factor PC 24/7, feeding a dedicated amp with its own volume control, but that kinda defeats the whole portable dongle thing
(FWIW, I'm seeing more reviews of other DAC/amps claim that the default gain is just too high for most phones in the 16-32-ohm range, and that's the majority of consumer-oriented headphones/IEMs on the planet in 2016 - somewhere in the quest to drive niche products that appeal to 5-10% of the market, manufacturers seem to have overcompensated in the gain dept - at least IMO)