HD650 or HD598, honestly forget they’re even there. Only nuisance is that the HD650s have a really low clamping force so if you lean back in your chair, they kind of slip back and make the sound quality worse. Regardless, when upright, it ain’t an issue and they literally just disappear after a while and you forget they’re there.

When I went from my 598 to 650 the improvement was quite noticable. Biggest thing is that the bass and lower frequencies on the 650 sound much more prominent, but also clearer. Also, yes, amp absolutely required for the 650