LCfiner said:technically, all you need is the E9 and you can hook it up to the headphone out port from your iMac.
but you'll get better results if you use an E7, which has a DAC, and hook that up to a USB port on your iMac, bypassing the Mac's internal DAC.
You don't need to use an E7, btw. Any DAC will do and there ones out there that are better than the E7. but the E7 is inexpensive and integrates nicely with the E9 (which is a damn solid amp for the money)
Concerning the smaller, in-ear monitors, I would suggest the Westone line of monitors. two reasons: 1. They are comfortable and sit really nicely in the ear. 2. If you have the cash, the W3 is amazing (I used to own a pair) great for rock and pop with a slight emphasis on bass and mid-bass frequencies.
I don't know how well the other models sound but they all seem to be relatively well regarded. I do know that they all have similar shapes so comfort should be close between all the models.
The W3 might be cheaper due to the recent release of the W4. Unless the W4 isn't as good, I'm not sure, haven't bothered to read any opinions yet.