Late to the party.C'mon folks, let's think about acoustic coupling and use some science to understand why casters do not affect acoustic (boundary) coupling to any meaningful amount.
The acoustic coupling or boundary effects occurs where the spacing off of the boundary is a significant distance compared with the wavelengths being considered. Since the drivers are usually several inches from the bottom edge of the cabinet, adding 3" casters does nothing relative to <500Hz (didn't do the math, engineering guess) and for higher frequencies (not what is being claimed), it's not am constructive coupling but constructive/destructive interference and adding 3" to the path just shifts the frequency pattern slightly.
I don't think they'd affect the coupling; I think you need to be a few FEET from the floor for there to be significant coupling loss. May actually help to isolate nearby items like mic stands from vibration, though.
I don't think casters will affect the sound, nor will toe-in and camber.
But... personally I prefer a little two wheeled cart over casters, when I have to roll an amp over any distance. Casters get stuck in little holes and cracks, most notably going in and out of an elevator. Also, I can heap more gear on top of the speaker when I'm using a cart.
Casters are better if you're moving something around a small space such as a studio or basement rehearsal room.
I'm old, I have casters on everything, even my Bergie CN112. No problems!
QuorumUnless the casters are more than 2 feet in diameter there will be no audible difference in sound.
achieved in first 5 posts.