Easiest way to add some bass to stock 2010 stereo?

The stock 8 speaker stereo in my 2010 Jetta TDI sedan leaves something to be desired in the bass department. I want to improve that situation while keeping the stock head unit. What's the best bang for the buck here? I would imagine it would consist of replacing the stock speakers and/or adding a subwoofer.

From what research I've done on the 'net it looks like replacing the front speakers is problematic -- apparently there's a sensor for the side-impact airbags that prevents the use of deeper speakers. Rears may be easier to replace.

As far as adding a subwoofer, is that feasible with the stock head unit? I'm guessing that the VW stereo will not have an extra output to feed to a sub. If that's the case, how would one go about wiring one in?

It's possible. You should look into something like this:

http://mobile.jlaudio.com/products_cleansweep.php?prod_id=369

Although, I have no experience with such components. It's something I'll look into later down the road after my speakers are burned in.

On the older Mk IVs you could recode the headunit to tell it it was in a wagon rather than a golf and that improved the bass.

The stock radios come preprogrammed with various sound curves, so you just fool it into thinking its in a larger car and it will raise the bass level slightly.

The new one is probably similar, so that may be a cheap tweek you can do.