Need some help, Factory nav w/new alpine hu

I just got my 2004 performance z with nav non bose. First off I love this car but the stock radio has to go. I have read in other posts it's possiblt to install new hu without losing voice directions. I want to know has anybody tried to use an fm modulator to get the voice through the radio. Also does the nav wires that cary the voice output have enough power to push a small unamplified speaker. Thanks for your help