Thanks EdBrady,
Using DVD Audio Extractor I have the option to rip the soundtrack directly to 6ch Wave or 6ch Flac, so created a couple of test tracks and confirmed the format with Mediainfo.
Resetting the S/PDIF zone to defaults for Output Mode and DSP studio, it plays 2ch.
Disabling DSP studio and it refuses to play and complains my hardware will not support the format. Trying various options will not allow a 6ch Wave or FLAC files be played.
Checking the hardware using the OS (Windows 2008 R2 SP1) it passes DD, DTS, 41KHz, 48KHz, 88.2KHz, 96KHz and 192KHz sound tests. DD and DTS all trigger multi channel on the receiver correctly.
Attached screenshot shows the supported formats for the hardware.
Q/How do you have your zone setup to play 6ch Flac?