I inherited my brother's 2001 Montero XLS 3.5l. He had put a aftermarket stereo in it. He cut the factory harness to put it in. I am looking to add a new head unit, but know nothing of the original system. How can you tell if there is a premium sound system from the factory? It has the 4, 6.5" in the doors as well as the tweeters in the corner of the front windows. (The 4 lower door speakers are all that works, so I can already tell that something is not hooked up right. It's not my first radio install, but it's the first on this kind of system. I am kinda flying blind and would like to learn more about the original system before I start on it. Is there any way to find out about from the Vin maybe? From everything I have read abort the topic always refers to a factory amp. Did they all have a factory amp or is it just included with the subwoofer? What about number or location of speakers to help identify it? If anyone might know or can point me in the right direction, I would really appreciate it.