I have a 2012 xB.
I like the base radio. The bluetooth feature rocks.

So keeping the factory radio.
Can I add a powered subwoofer?

I don't feel like spending a ton of money on a radio. Just a little to get a nicer sound. The car is a lease after all.

So keeping this in mind.

What do you guys suggest?
New door speakers?
if so what model? Sony?
And what can i do for a sub woofer?
Does the factory radio support a sub?
Any documentation on that?

 

Actually some of your questions are answered in a post just below yours. But here are some also.

Yes, your stock HU will support a sub. There are sub preouts on the back.

As far as what speakers to get for the doors and sub, you need to know what your budget is, and if you are planning on installing it yourself or someone else and how much that will play a factor.

I just recently upgraded everything myself except the hu cause like you, I really like the blue tooth as well as the other functions that work well.

 

I can do it myself as long as I have wiring plans.

I've done an install on a prior car.

I don't think I want to spend over 200 bucks if I can help it.
My first thought is a powered woofer or tube.

 

If you want a great sub for the box cause i had one.

http://www.ebay.com/itm/150852072653...84.m1555.l2649

http://www.ebay.com/itm/150852648936...84.m1555.l2649

ran that setup till i got my new 12's good soud very clear.