Honda Pilot factory system

I have a 2005 Honda Piloy with premium sound. It comes with a sub woofer from factory. I am adding an infinity amp with infinity speakers in the front and rear doors. I was going to change the head unit but was told by a cruthfield.com tech that my subwoofer will no longer work if I change the head unit. I think the factory woofer is enough because I don't really want a lot of bass. If I change the head unit is there a way that I can keep the factory bwoofer working. I believe there is a factory amp for that sound system. How can I rewire it to keep tht woofer working.

You can get a very small amp to power it up and it will still work good.  Jensen (I know, its Jensen) makes a small 50 watt amp which is about the size of  a DVD case that I've used before, with great success I think it runs about $30.  There are others out there that will work, the one key is to have one with a LP crossover, other wise you can get a cheep coil to do the trick.