All available aftermarket adapters should work for basic non-ipod mp3 players. Even the ones made for ipods usually have rca jacks in them. To get a headphone (3.5mm) jack to plug into your mp3 player with these adapters, youll have to get a patch cable for it too. It looks like this and will plug into your mp3 player and run to your adapter.
All the aftermarket adapters should work with navi headunits, but don't quote me on that. I have the SNHOND3 because I don't have an ipod, but I also dont have navi. Anyway, the connector is the same in the back of the headunits, just the location is different, you will probably have to pull out the whole headunit to get access to it, which isn't really a hard thing to do. Check out this thread, page 4 post # 51. It describes the steps to take for installation if you have a navi model
