Well there are 2 options that you have and both will work fine.
1. You can keep the HU you have now and run a cable to the battery, ground, remote like with a aftermarket HU but then you need your aux cables. To use them with a stock HU you need to buy Scosche SLC4 Four-channel line output converter at Crutchfield.com and this will give you your RCA ports.
2. You can upgrade your HU and run once again battery, ground, remote but instead of splicing you can run your aux cables directly into the aftermarket HU.
It's up to you if you want to replace it or not. If you are looking into using your iPod for listening to music in your car I would go with a HU with a USB port.
