How to add a subwoofer to my system?

I currently have a set of Mission 765 speakers that I absolutely love. However, they lack some low end for my rock and hip-hop tastes. For jazz, piano, guitar and vocals, I am quite content.

Should I run a powered subwoofer? I was thinking about using my amps' "speaker B" connections to add one or two subwoofers into my listening room without seperate amplification. Has anyone tried this?

I would like to setup something that doesn't require me to adjust the subwoofer to every other CD I play, no matter what volume. I just want to turn it on for some music, off for others.

What are some good ways that fellow Gon members have setup your systems with a 2+1 or 2+2 configuration?

I look for deals and I am on a strict budget. I will most likely spend less than $500 on this venture by building my own or waiting patiently for a good deal on used equipment.

Thank you,

T.J.