you don't need to change amps and speakers to change the head unit. You can buy any head unit you want, and as long as you get the right wiring adapter (Scosche VW01) and antenna adapter (Metra 40-EU10) you'll be fine. I also installed a JVC, and just make sure you use the PRE-OUTS instead of the amplified SPEAKER outputs for your speaker connections --

good luck!