[deniall83]

  Low impedance IEMs with an amp with an output impedance of 28 ohms (or 120) doesn't really make sense in the first place.  I notice less of a change in volume when I change the switch between Low and IEC when I use lower impedance headphones.  There's definitely a difference when I use 300 ohm Senns.

I realize it's not a good match but I needed to to test the amp was working properly as I bought it used. Surprisingly, they sound very good. My PL50's however sound awful. I'll be getting my HD600's tonight so I'll test them out.