Herbies Pucks floor spike protectors...

as I recall OP has 5a. I have used the Vandersteen spike shoes with five A, 7’s and the amps which are also spiked on both tile and hardwood to good effect. they are machined w felt and fit your cones, reasonable for made in USa, available thru your Vandersteen dealer

You guys will laugh,but I have little carriage bolts from the hardware store screwed in instead of spikes with felt pads on the bottom.Cheapo adjustable gliders:)

@jtcf ..I remember those days, couldn't afford something and my mind kicked in for a inexpensive work around. Thumbs up.

Several good suggestions made by all above. Take a look at all the products for speakers made by IsoAcoustic's in order to get a feel for other ideas. 

 @jtcf bravo !!!! add a nut and you have locking adjustable !