Actually the NAV uses exactly the same stereo system as the non-nav, but with a 4-disk CD changer instead of a 6-disk one. And of course the head unit isn't the same since it's integrated with NAV, but I seriously doubt there's any difference in sound quality.

All Camry Hybrids, and all Camry XLEs, come with the 440W JBL sound system as standard.