I don't think it's all that common. The EP350 didn't budge, but it also doesn't extend below 20Hz like the Sunfire Signature. I think this problem is specific to the Sunfire... it's fairly heavy, but it's also very powerful and the driver excursion is extreme. All that EMF to do what it does in a small enclosure translates to it wanting to move. The pre-installed feet are definitely too slippery, I don't know how you'd use them effectively on any surface (too slippery for hardwood, way too shallow for carpet). The second set of feet included are much better, but I've still got some movement.
It wouldn't bother me all that much if I weren't about to leave for the Kentucky Derby. Part of the enticement for the house sitter (a good friend) is our A/V system, which he enjoys. I'd be really bummed out if I returned from the Derby to find the subwoofer had gnawed away at my drywall or the driver had been bouncing off of the wall. I've only had it a few days, I want it to still be pristine when I return but I want my house sitter to enjoy himself.
I'd bet that the EP350 feet would work wonderfully on the Sunfire Singature for me. Hmm, I wonder if there's some way for me to order EP350 feet without ordering another EP350... I just need the rubber, not the bolts.
