Yeah, i have this same issue. Before i searched and found this post i reflashed my n800, paired the headset then played some music. It was mono but still ok for me, then i began installing apps one by one and as soon as i installed the fmradio the sound through my headset died.
Thanks. Yeah, I know all about the AD2P support issues. I was just having a problem getting any sound to come through my paired headset... After restarting my N800, everything started working.