Your problem may be that the audio return from the TV to the AVR via optical does not pass the requirements for bitstreaming multichannel lossless sound. That can only be done via HDMI all the way through, or via an analogue decoded signal (after DA Conversion). You will be able to pass through 2-channel audio and compressed (AC3/DTS core) audio though, up to 6.1 for DD-EX and DTS-ES.
Your other streaming player only reads the core tracks and sends those only.
You might be able to replicate the configuration of the streamer, in MC, by setting bitstreaming to SPDIF only, because that is in fact what you are using (optical connection between TV and AVR).