Had the same issues, although my amps are only around 120 lbs. each. My main speakers are 450 lbs. each, though and a mistake can end in a loud and damaging crunch. Suggest that you rent a stair climbing hand truck with strapping to move them. You don't need to buy them - any rental shop will have them for regular moving.
PS - make sure that the amp location match your speaker wire length before you return the hand truck.....
PS - make sure that the amp location match your speaker wire length before you return the hand truck.....