Quadfather
Headphoneus Supremus
The sound of the AKG K812 PRO is more immediate relative to the more distant HD800. AKG K812 is also slightly fuller sounding and less relaxed in its presentation.
I had both side by side for some years and although both are very good (superlative in some regards) I've gravitated more towards the AKG.
I have been listening to my K812 more than any of my other headphones lately.