What speaker system do I have, specifically?

I have a 2005 Mitsubishi Montero Ltd.. I know I have a Infinity Gold premium sound system with 7 speakers, but I need to know what kind of amp I have, how many watts it is, how much it can handle, and what brand it is... I am wanting to replace the 8 inch sub, that was pre-installed, with a cheap Walmart sub (Just for now) specifically a 12 inch Pioneer.