Fire TV HD audio question

Decided it was time to consolidate and retired my Roku and HTPC.
Ive used the HTPC pretty much daily for years with Kodi and it has been a good experience, but recently got to the point that running Windows for an HTPC that I only use for ripped content was overkill. Windows updates, power outages (Florida storms!) having to reboot or repower, a somewhat loud power supply fan…and of course the geek in me that loves new tech.
All issues that could have been worked out…I even had convinced myself to keep it and lose Windows in favor of Librelec.
But in the end the draw of one simple little box that is silent, small, uses little power, and consolidates my streaming services was too much to resist. So far its been a great experience. Not quite as fast as the chromebox in the bedroom, but pretty snappy.

My question, (and I was aware of the issue coming in)….is why doesn’t HD audio in Kodi (or SPMC) work on the Firetv but does on the shield?
Is it a hardware issue? Something Amazon crippled in software?

Thanks in advance…I searched but couldn’t find an answer.