More listening without swapping instantly from can to can, I am starting to understand the ROOMFEEL. That slightly hollow sound does translate to what you would hear with speakers in a room while the senn 280s have a more standard headphone midrange. The slightly boosted upper midbass on the NAD does bother me a little bit though because it muddles the mids a little. I'll listen to more music and report more later.

EDIT: I still prefer my Sennheiser HD280pros overall even without taking price into consideration but the NAD kills the momentum

The 280pro doesn't really have audible bass distortion if you speak of a clipping sort of distortion. I mean I can turn it up to ear splitting levels and the bass stays composed.

I don't know what you mean about the hollow mids when talking about the 280s. I don't hear it. Maybe its dependent on seal/headsize? Not sure

EDIT: Oh maybe you mean the closed headphone sound when you speak of the hollow sound. The dt250-250 has less of it due to the velour pads drying up all the reverb. Thats not what i meant though by the hp50s hollow sound. With the hp50, the hollow voicing seems to be deliberate and gives it that 30 degree angle sweet spot ala loudspeakers in a room type of thing. The hd280pro has none of that. The senns sound relatively flat in frequency response and more true in timbre in the mids as if the instrument is in your ear instead of being put in a room acoustic outside of the recordings own acoustics.