i was wondering if possibly you can add an external dvd/cd drive so you can listen to an audio cd while navi is on....

I don't recall if pioneer has made a single disc add-on in a while, but i am sure any of the ones they ever made with a p in the model number would work. you can definately find a cd changer, if cd is a must and nav disc removal is out of the question

DVD player: http://www.pioneerelectronics.com/pna/v3/pg/product/details/0,,2076_310069874_307126641,00.html

Or you could just run a CD changer...