Haven't heard the Shiit stuff. Don't get too occupied with raw power.... Neither the HD800 or the 650 needs wattage monsters. The LCD-2 isn't that hard to drive, wattage-wise either.
I always found the HD800 painfully bright, so if you have a brightness issue - HD800 + LCD-2 is a nive route. PS: LCD-2 rev.1 is easier to drive, cheaper 2nd hand and has a sweeter sound.