And yes, driver variations are a thing. I had two DT990/600s recently at the same time (along with a 990/32 and 990/250). One was more bassy with warmer/thicker tone, but distant mids. The other was pretty neutral-ish (for a 990), with more air, and closer to neutral mids, and larger soundstage.
Edited by Mad Lust Envy - 11/20/12 at 2:46pm