how do these subwoofers sound?

They're decent, and a bit above average. The unit itself is physically light for how it looks. I have no doubt that better aftermarket subwoofers (there are two inside the container) can be exchanged, and will sound better.

I'm not impressed with it at all. I want to replace it, but there are so many issues with finding anything that will work with the Bose head unit.

If you don't have the spare wheel/subwoofer housing Screw really tight it vibrates like crazy and resonates through the body which sounds cheap and nasty... Once you really tighten the screw down the sound is well above average... Not perfect but a lot better than some other base systems I have seen..

In my opinion, best sounding stock stereo system while stationary... Unfortunately the bass goes out the window while the car is moving.

My 2012 Honda Civic EX-L's premium sound system sounds better then this and it doesn't have a sub-woofer. Bose is totally over rated.