According to sources on VW Navi the subchannels are not available on the RNS 510 unless you have a C unit. Most of the RNS 510's in the 09-10 Tregs were A and B units. It is a hardware change on the C unit that allows for subchannels, not software. So no worries on how to access them since you can't anyhow.
OK, if I can't have it then so be it - but if I had a 'C' unit, how would I get to the subchannels? I have no easy way of knowing what hardware I have, so I can only hope that since my car is a very late 2010 build date it isn't impossible that I would have a 'C' unit, but with my luck it will be the very last 'B'.
If we set aside using a VagCom or pulling the unit is there a quick way of telling that I am ignorant of?