Neither of these things is correct.
said by wiz561:Sideloading the Kodi app to the firetv "voids the warranty"....at least I'm pretty sure it does.
Sideloading is perfectly fine and tons of people buy the FireTV just for Kodi. Sideloading is a perfectly normal thing to do on any Android device.
Running the software a certain way has no effect on the warranty, because the warranty is on the hardware, and the software can be restored.
If you're extra paranoid, you could even remove a sideloaded application or factory reset it before sending it in for a replacement in the event it breaks.
said by wiz561: A box that could decode these things probably runs about 200 bucks (new).
The Raspberry Pi supports hardware MPEG2 decoding (and can run Kodi). They cost $35 and then another $3.65 for the MPEG-2 license.