I've used Belkin surge suppressors in the past. I bought the highest joule-rating suppressors I could find. I heard no audible difference over plugging my rig straight into the wall.
I live in the high desert of Arizona, where we have monsoons from about July 4th through labor day weekends. We also have alot of brown outs during the summer. I decided I wasn't comfortable with just a surge suppressor, so I started doing the requisite hundreds(!) of hours on the available conditioners. Eventually I settled on the just-released APC S10. Now my rig sounds better than it did before. I never believed in the "grunge in the power affects your equipment's performance" but I'm guessing there must be some truth there because I do hear a "cleaner" sound now (for want of a better term.)
Will you hear a difference on your sub? I don't know - my sub's power cable isn't long enough to plug it into the APC, but I wouldn't expect much impact in the sound at that low range. I do know that I would expect to feel *much* safer with my audio gear plugged in to a unit that cleans the power, regulates the voltage, and protects the unit from spikes, brownouts and power outages.