The “channels” setting is how many PCM channels it can output to. As per your logs you equipment is reporting support for only two PCM channels.
====================== Audio Cap =================== k3dRrf31
CodingType MaxChannels SamplingFreq SampleSize
PCM, 2 ch, 32/44.1/48/96/192 kHz, 16/20/24 bit
AC-3, 6 ch, 32/44.1/48 kHz, bit
Dobly_Digital+, 8 ch, 32/44.1/48 kHz, 16 bit
MAT, 8 ch, 48 kHz, 16/20 bit
DTS, 6 ch, 44.1/48/88.2/96 kHz, bit
DTS-HD, 8 ch, 44.1/48/88.2/96/176.4/192 kHz, 16 bit
---------------------- Audio Cap END --------------- k3dRrf31
That setting does not affect bitstream/passthrough. It affects anything that isn’t bitstream.
Hmm. How exactly is your hardware connected?