Best vibration isolation for speakers on carpet?

Well if you feel ambitious  but a plank of very dense hardwood. You can find two inch thick purple heart quite easily.  Drill and tap three holes in it one in the front and two in the back. Put inserts into the holes and build some ready rod spikes with nuts on the to so you can level the speakers from the top. Measure in the stands you have built and level them your spikes that come with the speakers or I use disc's that cam with my speaker stand place them two at the front  on at the rear measure  the speakers on the stands. Then check out the level  on the speakers and from side to side the angle on each the toe in compared to each other etc. You have a system  that cam be adjusted  easily  that will anchor the speakers to the floor everything will be wonderful.  

Regards

I’m really happy with the Isoacoustics Gaia’s. I believe your speakers would use the Gaia 3’s and their carpet spikes, or you can do what I did and put everything on some granite slabs. 
 

+1 for Townshend speakers bars. I use them under my Harbeth M40.z Anniversary.  More difficult to adjust than the Podiums but sema results.

I have vandersteen quatros which are a big heavy speaker. I had leveling issues and bass control issues. Started out with the gaia with speaker discs. Midrange was magical but bass still to heavy and still hard to level. I called Richard vandersteen and he told me to get some granite surface plates. They're 3 inches thick and 18x24 or so. They weight an absolute ton but when I put them down they flattened the carpet and made it easy to level the speakers. The speakers are still on the Gaia but are now much more functionally isolated from the floor. Sound is amazing. Looks pretty cool too

Use butcher blocks and gaia isoacoustics

 I used the isoacoustics carpet spikes and didn't like them they were a little unstable. My speakers are very stable now and they are about 80lbs each.