I purchased that Aux cable for my MK1 RNS-E, all I had to do was plug it in, use VCDS to code the AUX function (add 4 onto the second for last digit under 37 Navigation, 07 Coding) into the unit and then hold down the Radio button and Setup button together to reboot the RNS-E and it woks fine
I do find the AUX input very quiet though so the volume has to be cranked quite loud to hear it