Plugging powered speakers in....??

Seeing that we're only talking about BASS, and not midrange/tweeter, you're fine plugging in the speakers to your outlet for best sound! There's really not going to be any significant improvement going into any filter or conditioner. INfact, you'll likely only LIMIT DYNAMICS!!!
Also, there should be a fuse for the amps in the subs, and I personally wouldn't sweat the surge protection any.
Worst case scenario, you had a lightening storm strike, and you blew the amp on your woofers. NO biggie...I'm sure it would be taken care of by manufacturer

I have my powered sub plugged, along with everthing, into my Audio Magic Stealth. Don't neglect your sub. The difference, while suble in the beginning, becomes much more evident through time.

Monster makes a filter just for subs that plugs into your wall outlet. I think the model number is SW200. I think this should be the minimum you consider unless you want a power surge or lightning strike to take out your powered subs.