Senna74,
I wanted to stabilize the speakers and raise them slightly. I tried outriggers on the front and back and settled on the front only. I kept the stock spikes in back. This tips them back slightly which helps the imaging. They even took back the back ones even though I had installed them and they had some scuff marks. Also, they are adjustable so you can level the speaker. The original spikes are flimsy and it is easy to ruin the threads. The only catch is I had to go to the local hardware store to find the exact bolt thread to secure the outriggers to the plinth. No big deal. I highly recommend them. Here is the website:
http://www.oregondv.com/Outriggers.htm