I sent you the logs by email. One is from a 4.2.1 CM ROM (nothing happening at all), the other log is from a 4.1.2 CM ROM (DUN says "Error"). Both using the same Andromadus kernel.
In the meantime I got it (partially) working!!! At least with the 4.1.2 ROM. I think it is a maybe related to this other thread viewtopic.php?f=41&t=598
When I tried to connect it, I was watching the RNS510 display, and there was a short message saying something like "BT connection not possible." I was wondering, because Audio was already playing and rSAP was established as well. I was looking at the phone settings of the RNS510. I found one setting called "Authorization" under the "Modem" settings. There I had to grant access to my Desire S for the modem. After another reconnect the RNS showed a message like "BT connection not possible, Audio connected".
So I deactivated the "Audio Player" setting in my phone's BT settings. I also found a setting in the RNS to deactivate BT Audio Sources. I also deactivated this... and... et voila! DUN connection established! with active DUN, I see a small data icon with arrows in the RNS display, instead of the little iPod icon that is there with the BT audio connection.
It seems that the VW RNS510 cannot handle BT Handsfree/rSAP, Audio and DUN at the same time. That's a pitty!