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

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.  

Hire a couple of college kids--they need the $$!

Cheers!

Okay troops, how do you do it if there is no carton as in an in-home audition of a preowned amp, say a large Krell or Pass 350?

I actually have 100lb Emotiva XPR-1 amps that I move around when I rebuild them.  I use a standard hand-truck, but put a small hand-towel on the bottom plate.  Tilt the amp on so that it is on it's side and wiggle it onto the towel.  Strap the amp to the hand-truck if necessary.