You know, in all of this, I'm kind of wondering what it is you are trying to achieve with this setup? What are you doing with all this gear you have managed to acquire?
Most people use a surround A/V receiver of some sort, or a decent audio pre-amp when they are going with external amplifiers.
A surround receiver will decode surround sound properly and has a number of room correction capabilities built into it. Not many cheap ones support external amplification.
For a good two channel setup, a stereo receiver or preamp will often handle digital audio inputs nicely and provide multiple source selection and volume control from a remote control.
But, you can go straight from a source of some type (PC?) to a amplifier and then to speakers.
It appears that the Polk PSW303 is powered. That's according to their website...
PSW303 - Subwoofers | Polk Audio®
Easy way to tell for sure?
If your subwoofer has a PLUG ON IT it probably is powered! (or you might be a redneck)
It's listed as a 220 watt amplifier with a 8" driver in there. You aren't going to likely get a lot of room filling bass with a 8" sub, but it will help the low end a bit.