the obvious answer from some of the folks here will be to check the quick links. that being said, i've done that and wouldn't mind seeing more detailed instructions for this particular install (RNS-E and XM). Hopefully someone will chime in with a link as I'm sure this must have been done and documented before.
Since this is the MMI Forum, not RNS-E Forum, at least one of you is looking in the wrong Forum!
If you have a new A6, new A8 or Q7 then this is the Forum to look in because those cars have the fibre-optic based MMI system.
If you have an A2, A3, A4, old A6 or old A8 then you should be looking in the DVD Navigation Plus (RNS-E) Forum because those cars were (or can be) fitted with the RNS-E - I think that's at least you, sfoperator.
Well, just to let everyone know, I retrofitted Nav and XM at the same time and it works great. I didn't have to reprogram anything it just started up right away. If anyone has any questions on how to do either installations, please let me know. I would be more than happy to help.