Spikes or Spikeless

With a little finessing and tweaking of the spikes, it should be very stable through the carpet and into the concrete.
You need spikes that are long and tapered sharply to get through all that padding. I made some platformes for my speakers with adjustable spikes because I have carpet on top of wooden floors. The platforms gave it some mass to clean up the lower end. But with concrete floors, that should be plenty of mass.
If it takes to much of the fullness out of the bass, just inch it closer to the wall to help fill it out.
Take small steps so you don't get to much bloom in the bass. It's a PITA, but when you nail it, all will be good.

I have had good luck with spikes over concrete,with an area rug under the speakers and 1" thick Maple between rug and spikes..Spikes grip into Maple and are stable with the weight of the speakers holding everything down..The Maples is just cut 1" thick, 2"x 2" square under each spike.....

Speakers with four feet are a PITA. For all my previous speakers, I had custom Sound Anchor stands made, and those guys know the benefit of a three foot base. There is no need for the constant adjustment. My current speakers came with Sound Anchor bases the manufacturer has made for them and unfortunately they have 4 feet. Fortunately, they are easily adjustable and lock into place, but still I find the need to occasionally go back and readjust, maybe because the spikes are drilling into the concrete just a little over time under the over 100lb weight. If you have an option, and you can make the speakers stable with only three support points, IMO that is the way to go. As to your question, I have tried SA cone coasters, Audio Point cups and spiked directly into the floor on my carpet over concrete and I think spiked is best. On hardwood, I like coasters or cups with Herbies Big Fat Dots under them.

How heavy are your speakers? How thick is the padding and carpet? Have you tried your speakers with and without the spikes?