Similar Question I was Asked at Ipodstudio
It appears that gain setting is not adjustable - so how would this amp do with low-impedance/high-efficiency IEMs like the Westone UM1, Ety ER4P, etc?
Hi Laxx the C&C Box will ajust itself to the Lower impedance using the
Sure Um1 and also again the ER4P inear Phones
The Sony Headphones I use have a Impedance about 24 Ohms @1Khz
About the same as the Sure UM1 @25 Ohms and the Etymotic ER4P @ 27 Ohms.
And it Drives it very Well..So Gain setting is Really not needed with
using the C&C Box Amplifier..With using the Um1 what you will find and
hear is a higher increse in sound Volume due to the higher Sensitivity
of these Phones that you Mentioned here..But were not talking a major increse
just enough that you would find the Volume control turned a bit lower
then Say with using my Sony MDR-V900..Well Seing they are inear phones
Maybe a good Notch Lower..Ok..So Laxx I would be very Surprized if you could hear any Hiss.This Amplifier is Dead Quiet..