I am looking to upgrade the speakers in my 2012 MX-5. I already updated with speakers I had laying around but figure if I put better ones in it may sound better. Currently I have a JVC AV60BT Head, Polk Audio DB651 Speakers in the doors powered by a 4 channel sony 75 watt amp. I bridged the 2 rear channels of the amp to push an Apline Type-R 10" sub in a small sealed inclosure. With the exception of the head unit I had all the parts laying around from previous cars. The MX-5 comes with factory components in the doors. I would like suggestions on replacing the Polks with a decent set of components. Let's keep the budget under $150. Since there are factory components in the doors does that mean I can just connect the new component speakers to the existing wires? What about the crossover that comes with the new speakers? There are 4 wires in each door. 2 for the tweets and 2 for the woofer. Thanks for any advice.