This isn't a question about how to install Rockbox. Please try to read our guidelines in each area before posting.
As well, if your search didn't turn up anything, and it's not mentioned on the accessory protocol page where we ask everyone to put their experiences, you should just try it. By the time you've read this message you could've installed Rockbox, started your car, tried it, and if it didn't work, uninstalled Rockbox, and updated the page so others could know.