I'm thinking about purchasing the Star Wars blu-rays, which have DTS-HD MA 6.1 audio tracks. How will the model 975 handle a DTS-HD MA 6.1 audio track if I have a 7.1 speaker layout? I'm not planning on using any post-processing (Dolby PL IIx etc.) Will my 975 mix down the 6th channel into the right and left surrounds, or will it matrix the 6th channel into my rear left and right speakers?

Does anyone know?

The mono surround-back channel should be played back through both rear speakers.