I've owned 3 different HD800s from the 14xxx-19xxx rang and they've all sounded identical to my ears-only changing as the upstream gear changed. That said-there's already another thread discussing this :
The two HD800 I compared were plugged in the same rig. They shared quite the same signature for sure. The Demo model what a tad brighter than mine though . A friend of mine was there and agreed with me. We tried to use the two HD800 in order to A/B my MG Head VS a trafomatic Head one and we perceived more brightness from one rig. then we plugged the two HD800 in the same amp ( the MG Head) and we could still notice differences. We stopped using the demo model immediately. Our interest was to compare amps not cans.
Its possible that hes just being nice and agreeing with you so you dont look loony
Im just teasing