Just incase anyone in the future comes across this thread -- I do now have this working!
I don't exactly know what I did, but I do know at one point today (after posting the original message), I recycled the power (took battery out). After I did that, everything seemed to work fine.
So, the Belkin Bluetooth USB Adapter does successfully work with the 8700c. I keep it (the 8700c) on my belt clip, and as I walk up to my computer, a few seconds later it connects with my Desktop Manager and syncs, and message redirection stops for the time being (until a few minutes after I walk far enough away).
Hope this helps anyone in the future!