I'm currently running Frodoplayer as the carpc frontend with Destinator 2 using the "ExternalDest" written by confused.
It starts destinator and then used the mini-mode of Frodo to allow you to use both at the same time.
Previously I was using MediaCar with Destinator 2 and it embeds into that quite well. Just can't change the music/volume/etc without coming out of the GPS screen and back to the music screen.
At the moment I'm sticking with Frodo cos it's being actively developed, whilst MediaCar has come to a halt.