I got an HD650 a week before I got a Salnotes Zero and they nearly sounded identical to me outside of the better bass of the Salnotes. I've made my case for keeping the HD650 because they are infinitely more comfortable to me for longer use than the Salnotes, but I am enjoying how similar they are to me and having the option to use each for when the situation is right.
You can't deny the bass though! Fortunately you can EQ the HD650 and get a bit of that bass back. My experience with HD600 though is that doesn't respond great to greatly increased bass EQ, as in I don't find it very detailed/defined bass after EQ. Your HD650 will be a bit different to my HD600 but there are similarities, but HD600 was very nice tonally after putting in something like a +3dB Low Shelf at 70Hz, it didn't seem to like an Oratory EQ. For the HD600 I liked the pure unadulterated nature of it with only that little bass shelf attached, which is contrary to my normal way of laying on EQ to my other headphones where I modify everything. HD650 is different though, but quite similar, so you might benefit by just putting on a little bass shelf, probably just very slightly less bass EQ than I suggest given the differences between the two headphones in frequency response. I just feel that way about the HD600, I don't think much should be done to it, albeit it's not my favourite headphone.