Hey. I think it depends. You can actually bend the headband of the DT1990 as well as that of the HD600/650, so the clamping force really is up to you. For instance, I have my HD580/600 very loose on my head because I wear glasses and having less clamping force is better for me. Most others would actually prefer to have even more clamping force, and a stock HD600/650 is basically "death grip" to me, so... you can just imagine how far you can bend that headband. But the thing is, you have gotta be careful. The headband is made to be in a specific shape, and if you use too much force, it'll break. I'd say try sandwiching a stack of books with the headphone for a while and then progressively increase the thickness of that stack until the clamping force gets to where you want it to be. The reason why I'm saying all of that is because I don't think the DT1990, or any Beyer DT headphone for that matter, actually sounds even the least bit similar to the HD600. They are more like the opposite side of the spectrum. If HD600 is mid-centric, then any random Beyer headphone is very much the inverse of that. It's their house sound. If you want an HD600-like sound but with "different" comfort, I would actually suggest that you try something like the Audio Technica ATH-AD2000 or ATH-R70X, or HiFiMAN HE-400S (gotta swap in Focus Pads A) or HE-4XX (gotta wait for Massdrop to ship them) with some other alternative pads.