Connection to in-car audio

I have a 4th generation 32GB iPod touch which is not recognised when I connect it to my in-car audio system.

Mercedes state that the 64GB is fully compatible, but not the 32GB!

Is there a difference in the operating software between the two versions, or am I just being fobbed-off?

I also have an 8GB 3rd generation nano which connects but does not have full functionality.

This time Merecedes state that the 4GB version is compatible, but not the 8GB!! Any thoughts?

Thanks