I already have a Fiio E17 which I'm using with a Beyerdynamic DT990 Pro (250 Ohm). For my taste, a really awesome couple!
I'm thinking about buying a low impedance headphone, the Beyerdynamic Custom One (16 Ohm). Simply to own a headphone without facing the pressure to drive it via external equipment... Nevertheless, I'm curious if there would be any problem using the E17 regarding the high volume: 16 Ohm is the minimum amount to drive a headphone on the E17. I don't listen superloud to my music (volume 40 w/ DT990), but I'm pretty sure that plugging the Custom One to the E17 would generate superloud sound even at the lowest low of the volume which is 20 (volume range on the E17: 20-60).
Is that so?
....and the second question:
Is there a huge difference between using the Custom One with/without the E17 as DAC?
If I'm using the E17, I'm goin' to use it on a MacBook Pro 2011, a standard Dell PC, an iPod Classic 160 and an HTC One.