PCM vs multi-channel PCM with surround speakers not working on Nakamichi shockwafe

[snirmy621]

So I recently bought the Nakamichi 9.2 shockwafe system and have been setting it up. I have noticed a couple quirks I need clarification on.

I am running the sound from my PC (windows 10) to the soundbar directly with HDMI and then to the TV with HDMI ARC. I have noticed that when I select anything other than stereo in my windows sound panel under speaker setup/configuration (either 5.1 or 7.1) and go through the process of testing the speakers with the windows test sounds, I can hear audio from all my speakers appropriately. However, when I go to play any media (such as a movie), I get no sound from my surround speakers (side and rear speakers) - I only get sound from the front speakers. I also noted that my soundbar states "M-CH PCM" which I am assuming is multi-channel PCM.

In order for me to actually get the movie playing through all the speakers (side and rear speakers), I have to select a stereo setup under windows. It plays fine after that and I am surrounded with all the speakers working. I also noted that on the soundbar is just says "PCM" (no multi-channel). Same issue despite my playing a movie on PLEX or watching a blu-ray on cyberlink powerdvd.

Another weird issue is that I get this weird delay when playing audio through HDMI. I'll start playing something and the video will play but for the first 2-3 seconds, but I will have no audio, and then all of a sudden the audio will start working (but no lip sync issues). This is most pronounced with youtube videos when I watch a video and then go back to the home screen and select another video. But if I play videos or any media in quick succession, I don't have that delay/signal loss during the first 2-3 seconds.

This delay doesn't happen when I connect my PC to the soundbar with an optical cable. Also, using the optical cable, I don't have issues with the surround speakers not working but the soundbar just says PCM (no multi-channel).

My main question is, what is the difference between PCM and mulit-channel PCM. I assume the multi-channel is better, but for whatever reason, I can't get it working with my surround speakers. What would I be losing if I just stick with the optical out?