Sturds

Hello I was messing with my RX today as the front speaker was making a funny sound, I took the panel off and the speaker was blown. So I decided to check the rear door to see if it needs changed but it was fine, the main reason im writing this is that inside the drivers side rear door there is a small box that says "MPS DOOR" on it it looks like it has the same plugs as the ignition switch, is this the receiver/security system? Or is it part of the c-best system? Also where can you get OEM speakers for the lexus or is it worth it to just buy upgraded speakers?