I'm about to get the LG 65C8 (my 1st choice) yesterday but end up getting Sony 65A8F at only 7k. No excuse to turn down that great offer from clearance sale.

As long as gaming isn't your main usage for the TV, the A8F is definitely a good choice given the price. Congrats.
Cd/m on an OLED should not be compared directly to an LCD. There are differences in how they work, while the bottom line for cd/m measurement is get a unit output - how humans perceive it in reality is different. Our eyes are not meters, people often forget about this and care too much about numbers.

I'll quote this here from flatpanelsHD as it's already been explained several times:
If you are constantly watching full screen bright content (specifically sports or news), then a panel that can hit much higher peak brightness full screen is definitely a more suitable choice in a bright room. Otherwise, OLED is still the way to go - until MicroLED becomes mainstream.

I am still on a C7 so I cannot personally comment on the C8. My C7 passes through DD (also DD+) and DTS through HDMI ARC and also optical just fine. I don't however use any passthrough as I connect all my sources to my receiver directly for lossless audio.

According to reviews and also many personal users comments, the C8 also passes through DD and DTS through HDMI ARC and optical as well. Actually all DD and DTS signals will be decoded properly onto a 2.1 soundbar, it's simply a matter of the soundbar downmixing and folding in the center, left+right surround channels into stereo. There is nothing that doesn't decode properly, because if it doesn't - all you will hear is static and garbled noise.

HDMI ARC has never worked consistently and will never work consistently. There are simply too many issues with handshaking of devices. eARC which is supposed to fix all these teething problems haven't actually done much better either, at least from what I'm reading with devices using eARC.