Are the spikes too short and fat to pas through the carpet? Target speaker stands come with long thin spikes which are available separately, but I'm not sure about their thread sizes. You could check with one of their dealers. They also have a kit which includes the threaded inserts for the bottom of the cabinet, if you're not opposed to installing a second set of inserts in the bottom of your speakers.
Here's a link to a page that shows the kit (third item down on the page):
http://www.uhfmag.com/MiscAccessories.html
Here's a link to a page that shows the kit (third item down on the page):
http://www.uhfmag.com/MiscAccessories.html