Had a quick look. Roughly around the 20-30 Ohm range, which is relatively low impedence. In terms of getting the maximum output (note I didn't say audio quality) from them, you won't need an amplifier. It also depends on what your desk is like - some will have a high-impedence headphone output anyway!
The good news for you is that your in-ears are rated for pretty much any mobile device, which tend to be the ones that are mismatched. Your in-ears will produce their designed output with iPods, laptops, etc without any need for an amp.