Here's a better view to ignore compensation differences, first look at HD25 vs HD600.
Then my graph of HD vs HD600.
HD25 has the usual "sparkly" peak at ~9-10k which HD6/7/8 lack. So yes they are somewhat "dull" if you are used to that. But they can be played loud without piercing your ears. And um of course the bass is much more boosted so..
Edited by hekeli - 3/5/14 at 10:26pm