I wouldn’t put casters on speakers any more than I’d  put spikes on a moving crate especially when there are products like Herbies Gliders built for the purpose, but that’s me.  

Try threaded stem mount leveling casters from Footmaster. These will let you roll the speakers around on casters then drop them down on rubber pads built into the caster foot and level your speakers at the same time. What you have to do is match up the threads your speaker uses for its spikes to the casters. If they are not the same you can get threaded rod that changes where one end fits the caster and the other fits the speaker.

HandTruck 

Hire movers.

+1 Furniture sliders with adhesive attached to the bottom of the discs holding the spikes. This has made it easy to adjust the position of my 100+ pound towers.