I think it might have something to do with the amping (not exactly amping quality per se, but characteristic of the amp). My SA5K through my Marantz receiver and Sony receiver sounds exactly like Bangraman's account of SA5K's base: impactful and rather uncontrolled like a DJ can. Though the quality of the headphone-outs are contestable, I would claim that receivers weren't particularly at fault since there isn't anything abnormal about the sound of my HD650 through those receivers. When I used to own the DT880, the bass was indeed quite tactile with the Marantz. On the other hand, I've heard the SA5K with a G-Lite and it was quite detailed and fast, but of course there was less of an impact. I've also listened to the SA5K out of a SuperMacro Lite and SR-71, both of which focused on the detailed and fast aspect of the SA5K.