CD Mats

I have never heard a mat, but I would bet that none of them are designed to work with changers.

With CD's that have had nothing done to them, except for using Bedini Ultra Clarifier de-magnetizing before each play, the top of the line Marigo Signature 3-D CD mat, and the Herbie's Audio Lab Grungebuster 2 CD ring mat are quite audibly effective.
For great majority of CD's I prefer the Marigo, although the Grungebuster has the distinctive extra effect (call it a "feature") of seemingly shelving downward the treble brightness which afflicts a certain proportion of CD's, even when other aspects are better served by the Marigo.
In my systems, this favorable tone control effect has allowed 1950's era recordings now digitally re-mastered into "too bright" CD's to get back in play rotation.
May be peculiar to my systems, but others also have noted this taming of the shrill in my systems when certain non-audiophle approved recordings sneak onto a CD tray.

I'm using the Blacklight CD mat. When copying disc's using my dual tray phillips CD recorder, certain CD's won't copy even after multiple trys. I put the mat on, and voila, the cd copies. Must be doing something eh?.
I only hear a subtle improvement when playing music on the big rig tho. Haven't done a with/without test since I've improved the front end, I'll try to get to that next week.

Aurex claims that its mat will work with changers as long as they are the horizontal type. The SID specifically says not to use it with changers. Not sure about the other kinds out there.

I have tried a few, Blacklight, Ringmat and the Marigo signature. Only the Marigo made a worthwhile difference and that was very clear indeed and worth the greater cost. Unfortunately its only the costly tweaks that seem to work well.