The option #1;
Purchase carpet discs, but I believe the speakers would become wobbly, unstable.Less work, but expensive.

The option #2;
Use existing spikes from your speakers for the stone or wooden platforms, install Gaia pads on your speakers.
The option #3; (my favorite, because I'm a heavy metal maniac, who woulndn't give a fuck about the carpet)
Make nice big stone or wooden platforms and screw those bastards to the concrete floor through the carpet, then place your speakers on stable platforms.
When I found my sweet spots for speakers, I took gently wet rug, tilted the speakers and wiped the bottoms of Gaia pads, they're sucked to the floor.If for some reason, you'll have to move speakers in the future, gently and slowly tilt them, until suction gives up, don't you force it!!!
Are Gaia pads worth it?HELL YES!!!!!(Sorry about my English)