This is what I have been able to understand In TCL TVs so far: The C6K is the default. The Q6C is only available through exclusive online retailers like Amazon and it adds a “Common Interface Card” slot which can be used by some cable companies to give you encrypted cable channels instead of a set top box (this is a minor feature but it could be valuable if your cable company uses this technology). The C6KS is a “reduced” feature model to make the TV more affordable by removing 1 HDMI port, reducing the number of “zones” in the miniLED brightness, reducing the audio output by a small fraction, and maybe reducing the RAM as well which could affect future performance of the TV as the software gets more bloated over time. (I have added photos I could capture from online retail websites in India)
Does anyone have more insights to share?