How to physically move large heavy 100lb amplifiers easily (up and downstairs)

"Why wouldn't they show the guy with the boxes try to use it going up the stairs with the boxes? (even if the boxes are empty)."

If the boxes are empty, they may fall, if they are full he may not be able to pull the cart up?

Carry one amp with your left hand and the other with your right.  It's super important that you maintain your balance and not get your spine out of alignment.  Also bound up the stair steps two at a time to cut the total number of steps in half.

That’s how it works
https://www.youtube.com/watch?v=0PpNLD3TrdE
https://www.youtube.com/watch?v=huZ2ZnO2630

Just ask your wife or girlfriend to do it ;-D
https://www.youtube.com/watch?v=FXxdZoUzL6c
https://www.youtube.com/watch?v=rycfK_8o0lk
With the right tool, a piece of cake!

For heavy hauling, I ask the neighbor kids.  Both college football players.  For a 100 pound amp they would ask which one should come over to help.