I just upgraded from Bose IE2s to my first IEMs Shure SE215s. Right now I'm listening to them with a Sansa clip ZIP 4gb.
Don't know all that much about burnin but I have been using them for about 14 hours now. Still getting used to the difference in sound. I'm still learning about sound and science, there's a lot to read here. So far I'm happy with the SE215s, it's totally different listening experience. I hear a wider range of sound and can hear all the instruments without the sound running together. All seem to be pretty balanced.