The Mojo is driving an electrical load (headphones or amp), so no difference up to that point. The difference comes in that the impedence of headphones will change with frequency (they are a mini version of speakers), but I am not sure about the input impedence of amplifiers. The Mojo is happy driving low impedence phones such as shure SE846 (9 ohms I think) and high impedence phones (eg Sennheiser HD600 and HD800 are 300 ohms). beyer offer some headphone families with different impedences, eg the DT 770 pro is available at 16 ohms, 32 ohms, 80 ohms, and 250 ohms). With this design strategy, phones are basically the least impedence model, with an inline resistor added either in the headphone lead or the earpiece. Why all these versions of basically the same headphone? Firstly the 16 and 32 ohms are easier on the battery life of mobile phones, but this must be balanced by the fact that as the impedence increases, the control over bass notes improves - so it is swings and roundabouts. But this is digressing from the Mojo, I am sure that I saw posts by Rob Watts that state that higher impedence headphones draw less power than lower impedence models, but I cannot find them yet.