Especially now that they have added the two new EQ settings (which who knows what they are affecting...)
I'm pretty sure they are low and high mid. I've been playing with the EQ a lot over the last few days and it's amazing how much better the stock system sounds with some tweaking. You can really isolate the favorable-sounding bottom end without making everything sound muddy like before (since you can isolate 3 ranges of mid now). I was think about upgrading to a sub, but now I get plenty of bass and the clarity/quality is definitely passable.