Subwoofer or new speakers? - need advice

I currently drive Spica TC60's with a Classe CAP-100 Integrated (overkill or what?!). My room is 20' x 14' with cathedral ceiling. The speakers are on the long wall about 9' from the sweet spot. I used to listen almost exclusively to small group acoustic jazz and chamber music on CD and vinyl. Now that I've started playing rock, electric blues, and reggae I can't crank more than half way. What should I do? I know next to nothing about subs. What are the pros and cons? What are the logistics? I don't even know how they work. Some direction would be appreciated. I hate getting rid of the Spicas; I've grown to really love them (too sentimental?). Thanks so much for your feedback.