wiring, ’84 oldsmobile toronado

Hello all, I am new to the forum, but have poked thru the topics before joining... Now that said here is what I am looking for: I have an '84 Oldsmobile Toronado with a Sony Xplod head unit (200w max x4). I also have a pair of Sony Xplod 10" subs that I wish to install in the vehicle. Sounds simple right? Let me explain the rest... I have the head unit in (for some time now) and also have install a pair of of some dirt cheap 150W (@4 ohm) 4x6's up front and a pair of dirt cheap (250w x 4ohm) 4x10's out back. What I want to know, is since the head unit doesn't have pre-amp outs, how would I go about wiring the subs (with an amp of course, also crossovers if needed) to run the Rear deck speakers as well. The fronts will be run from the head unit since their minimum power is around 20W. I found another topic that may work, but want another opinion on this. Here is the other topic, sounds like what I want to do. https://www.the12volt.com/installbay/forum_posts.asp?tid=117673&KW=4+speakers+from+two+outputs Would this work and what wattage output would I need from the amp to run them all?

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