I have the K1000,the HD600, and the HD650. The K1000 is a very different experience. They have incredible detail and dynamics. The Sens are a more mellow warm and fuzzy sound. Not that they lack detail, they are just more distant. This is due to a stepped off high frequency range in the Sens, vs a relentlessly flat response in the K1000. I can (and do) correct the Sen response to something similar to the K1000. They still don't quite get the detail and dynamics of the kilo-k.
All three cans are shy in the low bass region. The K1000 is the weakest, with a rolloff at 50 hz. The HD600 are next best, and hang on a bit deeper. The HD650 have the most bass energy, but they have a broad peak around 80 hz which gives them an obtrusive and overly punchy bass that I personally find a bit obnoxious. Easy to iron out, though.
With the eq on, either Sen can produce bass that is flat right to 20, with amazing speed and damping (if the amp is up to the task). They also have the edge in comfort. They stay put when I move around. I have to sit still with the Ks.
With the eq, my HD600 are my most listened to cans, followed closely by the HD650. Pre-eq I was getting ready to unload the HD600 because of the shallow bass and the lackluster highs.
The K1000 I still dig out on occasion when I really want to connect to the music. They have an added complication as well. I can't listen to them long without a subwoofer. Missing octaves bother me.
gerG