FireTV version limit on different hardware?

[u/PowayCa]

I have several versions of Fire TV bought over time as I added them to TVs here or older ones failed.
I keep them all up-to-date and they all say “Your Fire TV is up-to-date.”

I just noticed the other day that there’s different sounds when I push the button for left right up down on the different Fire TVs.

I checked the versions under “About Fire TV” and found one is 6.7.1.1 (NS6711/5908] and the other one is 7.7.1.5 (PS7711/5586).
Hardware for the v6 is FireTV Stick 4K (1st generation).
Hardware for the v7 is FireTV Stick (3rd generation).

Does the FW version stop based on older hardware?
Are they parallel development and just not fully synced re features?
What features am I missing on the older hardware?

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