@doctorjazz here's a quote from Gavin:
The 450mW version of Geek will have plenty of power for your(average) buds. Do a quick Google search and find out the impedance. If it's below 60, again, 450 mW will be fine. Above that, I'd consider Super Geek. Above 300 and I'd consider Super-Duper Geek. Others might have different opinions, but those are my two cents.