Will a subwoofer add depth and clarity to my system, or just bass?

And yes!
Audio improvement its a neverending story!!! Its an addiction!!  :-)

So when ya ordering that sub plga? ;))

You have all lost me.  Guess I need to get a sound engineering degree to understand.  Wonder how you all learned this?  

Dave
I already bought one once and never again!!   :-) 
Larry
Well, even Im not a tech expert AT ALL, it took me about a couple of years, a lot of hours and mostly some not small cash to learn it the hard way and I think the only way.... Readind, buying, connecting, selling, tweaking, tweaking again, listening, more reading, etc.
If you like this hobby like me, you will do it without getting tired!!
Cheers to both of you

@plga - thanks for sharing your experience.  

I've often wondered if it's worth the trouble for me to pursue the bottom octave knowing that it will be difficult to get right.  Sounds like it can be done but be prepared for a daunting task.

For now, I'm going to keep it simple.