think it was so cold we all wanted to get into the cars to get warm, its this one gog
http://www.connects2.co.uk/Instructions/USB_OEM.pdf
I just use it to play MP3 via an SD card, its not very sophisticated but works fine and sounds as good as the CD, it also still allows use of the CD changer if i want, but as you have the RNS-E with SD slots not sure its what you want, I bought mine from Adrian on here as he wasnt happy using it with his RNS-E, as I say depends what you want to achieve I guess
cheers