HybridJack

I would like to upgrade my sound system but haven't had much luck getting information about what is in my car currently and where it is all kept.
For example, I understand that somewhere in my vehicle, there are supposed to be a couple of subwoofers but I can't find them.
If anyone can help me with extended information about the stereo system in my car, i would greatly appreciate it.
It's a 2009, RX400H with nav but not the premium sound.
I would just like to do a clean install and not tear everything up if possible. Any links to others that have done this sort of thing would also be appreciated!
It would be amazing to see if and how anyone has removed the cassette portion of the stereo and added in parrot, ipod or anything else that would make more sense than a cassette deck.
Thank so much for your time and help!