FeanoreanIt really depends on the amp - I have a few amps that work perfectly well with lower impedance headphones even though the amps have a 10 and 30 Ohm output impedance. However, I wouldn't try to drive anything below 16 Ohms with the Audioengine D3.... I ordered one and I am confident it will be just fine with IEMs.
koolpep:-) I'm not really worried as I only plan to run portable headphones with an impedance of 42 ohm and my RE0 which have a high impedance of 64 ohm for IEMs. So yeah I jumped on this drop as well.