Did some listening to my hd600s again. I listened to some dvds and cds of various genres and can now make a simplified analogy of how the hd600 sounds compared to my former AD2000 (shipped out today).
If we were to compare the two cans as if they were television monitors, the hd600 is closer to a well calibrated monitor with a little adjustment to make the picture slightly warmer than natural. Lets call the hd600s "filmlike". All the detail is there but balanced slightly on the warm side. The AD2000s are more like a High Definition monitor with a punchy/contrasty look but missing the details (ex. looking at clouds in a scene for example will make you see less grays in between).
In other words, sonically the hd600 has a softer, airier sound than the ad2000which in contrast has a more incisive sound where all the notes seem to be pronounced. The ad2000s are punchier at the expense of inner detail. The HD600s have better dynamic contrast which makes them very detailed. The hd600s are definitely a higher resolution can compared to the ad2000s on my modest system. The kicker is, these suckers cost far less than the ad2ks! Wow! Joy divisions music for example is detailed, fun, and doesn't sound irritating all at the same time with the hd600s. The same music is puchier but less emotional, less fun on the ad2000s because the mids tend to get irritating. Everything gets congested when all sorts of noises are going on in the recording. The hd600s split all the noises in their own space in your head and make everything so enjoyable to listen to. Now thats what I call a FUN can. I think when people call the audio technica AD series airy cans, they are probably referring to the seemingly fast bass response in contrast to the slightly fatter yet less impactful sennheiser bass. I can dig that but when a headphone doesnt get the timbres of instruments as well as cans half their price, thats a major minus for me. What makes the sennheiser airier sounding than the ad2000 is its extended highs and instruments floating around your head with a light touch compared to the heavier sounding (like everything is playing fortissimo) ad2000.