An aftermarket head unis one way to go, however, I updated my OEM Monsoon 2003 cassette head unit to a later model OEM Sat/Aux head unit. It allowed me to keep the OEM 6 CD changer as well as the newer head unit plays MP3 CD's and displays track info.
I now have a Aux input that I have a Belkin Bluetooth device that allows me to stream music/Pandora from my phone via A2DP and also have hands free speaker phone with audio via the car speakers.
I also have an OEM Sirius module to go in the car once the weather warms up and I have a spare afternoon. I have all the cables and connectors, I just need the time.
Not an easy approach, but it has everything except NAV, but if I use my phone for NAV while streaming Pandora the NAV commands will come over the car speakers while reducing Pandora volume.