[Nimbus117]

I changed my CDR23, amplifier and CD changer for a Pioneer 940BT satnav unit. I had the dash speakers and door subs factory fitted. I also added rear speakers and an Alpine two channel amp. I ran the front and rear speakers off the Pioneer head unit and the subs in the doors off the Alpine and sounds now amazing. The subwoofers in the door sound twice as punchy with a decent power amp. Functionality is greatly improved, just a nicer place to be. Total cost buying all the components, installing it myself and after selling the CDR23, amp and CD changer was less than $1000.
In fact it was $600 as I originally bought a used Pioneer D3 head unit first, then a Kenwood 5280 before settling on the Pioneer and made a healthy profit selling them both on fleabay. Up to you but you can do it yourself for not a lot with excellent results. I also fitted a reverse camera.