I never said bugster's AVR must be getting PCM, but the issue is whether it's 2ch or MCH. DD/dts can be 2CH too when re-encoded from 2CH PCM.
What's curious is we still don't know; don't all receivers tell you many channels are coming in, at the front display and/or GUI info screen? And many BDPs have GUI info display to show what track is being played.
It's worth getting back to basics.
1. Ensure that a MCH track is actually being played.
----If a BD has a separate old DD 5.1 (usually a non-Eng track), try that too.
----Try a DVD with 5.1 on the BDP.
2. Find out exactly what the receiver is getting, 2CH or MCH, next, DD/dts or PCM.
3. Try the Bitstream (unprocessed) option. The re-encode options just complicate things here.
4. Then if (3) still doesn't work try without HDMI...