I have the same issue with my Slingplayer. If I use normal headphones in the 2.5mm jack I get perfect audio sync. My bluetooth Jabra BT8010 does get the audio delay and there is no way to tweak it. As sad as it is, I just learned to live with it. I have had the issue with 2 previous windows phones,(touch pro and Treo).
Interesting that some people at XDA are not experiencing delay. The problem must lie with certian models/brands.
Bluetooth headphones with no delay for movies - xda-developers
Sarge