I had the Strato C for a number of years and just replaced it with the Strato K.
What I feel I gain
1.Cinematics. Played Eric Clapton Slowhand. Looks better. Noticeably better

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2. Ability to play movies if my Compact Server failed with a small config change
3. Strato K ran much cooler
4. 8K ready. Though I believe only one clip is available. But can test my projector

5. Black color
What I feel I lose
1. Strato C feels more solidly built. Heavier
2. Separate HDMI Audio port.
Overall, for me. I feel the first 2 points is sufficient to justify the change.