Lots of info and articles on this. It can be done, you just have to learn how. It isn’t just the FireOS either.
Thanks MIki, but after trying all the methods and therefore erasing Tivimate of all the customization I had on it a couple of times, I have given up.
I ordered an Nvidia Shield and will eventually change all my Firesticks to Nvidias.
Anyone wants a working, but crippled, Firestick 4K Max, 2nd De-genaration? For free, just pay the shipping.
I don’t blame ya. I have a Shield Pro and even it was a tad awkward to set up for recording to a “Removable storage” device, but a bit of learning and some configuration and works like a dream now. Happy Easter 
. I had 12 new 4K Max in sealed boxs and have given all but 2 away. Have fun and STREAM ON!!!
I just subscribe to the tivimate app but I got only 1700 channel because am using the HTTP link Troy gave out in his tutorial and I more channels.