As far as I know, BlueTooth's AD2P support stereo only, but I could be wrong. check to make sure your "surround" from BlueTooth isn't some kind of DSP automatically applied by you AVR.
Second, what transport are you using ? Analog, optical, TOSLink or HDMI ?
Third what software are you using ?
For bitstreaming, VLC, MPC-HC and JRiver work. Other software can do multi-channel, via PCM, such as Foobar2000. Apparently, it can also bitstream, but I haven't made it work yet.
There a few tips on
this thread, called "
Winamp, bitstream or passthrough". The OP never showed-up for his answer, but there's quite a bit of work in that thread which is related to your question, it may help you resolve your issue .