In short, HD 650 and AVI ADM9RS are very close to each other in overall performance with AVI may be being a bit better overall, in several aspects that too. But both are very comparable.
HD 650 is definitely lusher, sweeter and more musical though. Though there are lots of place where AVIs are very close or better than them :)
I prefer to listen to AVI over HD 650 unlike with Aktimates where I never listened to them and spent time only with HD 650 :D