What's there to explain? Dell gave the X51 a crappy bluetooth stack, end of story.
I don't have TomTom, I don't have the resources to help you with it.
I got the MS stack working with GPS10 and IpaqNav System. I got it working with and without the GPS utility (crap) the X51 came with. This was done several months ago, months before the the widcomm stack. Switched to the widcomm stack and never looked back ever since.
1. Paired the GPS device and clicked on "New Outgoing Port" which gave me the GPS port (com 8)
2. Opened my Ipaq Navigation System and set the GPS port to com 8 (same as outgoing port)
Ignore the GPS Utility Screenshots, you don't really need it.
If you are having problems with TomTom, others might help you with it. This is just to let you know that however crappy it is, it works with GPS out of the box.