car audio installation

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if you clean that message up I may try to respond with an actual answer...

Need some particulars before we can give you a definite answer: Do you have the 8 ohm sub or the 4 ohm sub? cuz I know that model polk comes in both versions. Also,what kind of 6x9s are "behind rear seats" right now? Bridge two of the amp's channels (probably the 2 rear channels) to power the sub, then use the remaining two channels to power the components in the front. Use the alpine's internal amp to power the two 6x9s in the back. Or if you want a simpler setup, just power all 4 of your speakers using the Alpine, and then power the sub with two of the amp's channels. If you chose this type of a setup, you'd have the advantage of being able to control the sub volume from the head unit (it has a non-fading set of preamp outputs), while still retaining full fade/balance control of all 4 speakers. To some people this is important, but others don't even care, so that's something else you need to decide on.