"On the whole the HT-21 is an aggressive headphone"
Wow, you weren't kidding. I'm auditioning a pair of HT-21s for an upcoming review and decided to take them with me to school to listen to music with on my lengthy break between classes, replacing my HD228s, at least for the day and the two songs I listened to with prominent snare drums were downright painful for me at the volume I felt I needed to play these at to cut down on the ambient noise of the cafeteria. This is mostly due to my inherent sensitivity to spikes in the upper midrange and treble (I'd call it sibilance but that doesn't really apply here), particularly those caused by the crack of snare drums.
The HD228s isolate a good deal better so I don't have to raise the volume as much but I think their more laid back sound signature is better for me in instances such as these which sucks because I really like these on the whole, perhaps better than the 228s.