The B22 is more stable, thermally and electrically. It is better equipped at handling hard loads like speakers (see this), and the parts are easier to find. I would not choose a dynahi over a B22.
They're really very similar though, brothers in the head amp world.
If only all that translated to better SQ.
Just a quick comment on this as well - no headphone is going to give you any soundstage, at all. The nice thing about headphones is their detail and separation, but when you've heard a good speaker system you realise what "soundstage" is. It's not possible from speakers attached to your ears.
Headphones can and do have a soundstage. It's small and intimate compared to speakers obviously, but that doesn't mean no soundstage exists.