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

An elevator would do the trick. I think they run about 50k. Or perhaps some type of dumb waiter if the budget or space is limited.

Would something like this work?

https://www.amazon.com/Shoulder-Dolly-Moving-Straps-Efficiently/dp/B00022749Q/ref=sr_1_24?crid=1FWQP...

 Yeah, use the straps but invest in half a sheet of 3/4 inch plywood and make the "perfect platform" for the amp (trimming required).

Buy a hand truck; it's cheaper than physiotherapy. 

Kent English of Pass Labs once had to move BIG amps up a flight of stairs. He walked them up it (in boxes, obviously), end over end. Not the easiest, but doable - as long as you don't let it slip!