I am actually really impressed with the upgraded sony system. I go the 10 speaker, 6-disc system option in mine (no nav).
After reading up, I pulled the sub out and opened the box and filled it with poly-fill as others have suggested and it did in fact make a pretty noticeable difference. I think for the price paid it sounds really well. I would have liked to have had a mid level control or maybe a separate sub woofer control along side the treble & bass controls to be able to finely tune it a bit better, but overall I am happy.
I like the fact that I won't be pulling apart my dash and truck to run wires etc to install all the aftermarket crap I normally would. I pretty much always install upgraded audio equipment in my vehicles but find no need on this one.