I know there are IR/RF extenders/converters out there, but I have no idea whether the Harmony 650 will work with them. The FLIRC Universal IR Receiver for the Amazon Fire TV is on sale for 13.99 at with free shipping. For example, I have several Roku boxes (XDS, etc.) that use IR and therefore work just fine with the Harmony 650, but I recently purchased (and subsequently returned) a Roku stick that uses RF and therefore does not work with the 650. If your devices use RF instead of IR, the 650 won't work with them.
The easiest way to tell if your device uses IR is if the remote requires line-of-sight access to the device (can't have the device hidden in a cabinet). Launch the Harmony software and add a new device as follows: Device: Media Center PC Manufacturer: Flirc Model: FireTV / Kodi / Plex. I have used the FLIRC to control an Amazon Fire TV box with a Logitech 650, Logitech Harmony Touch, and a Universal Remote Control MX-700 & MX-850. Most consumer media devices use IR remotes. Harmony setup for Kodi on Mac Add Kodi to Harmony During the setup. The Harmony One has an canned profile for Flirc, XBMC. Yes, you can use your TV remote control with Flirc as long as your remote control has. Sources: HRHR Prime with Charter CableCard. For me that is TV on, HDMI 1 Soundbar on, Optical on Video switcher On, Output 3 FireTV Home, Audio Optical. Buy Fuzzy a beer (Fuzzy likes beer) unRAID Server: i7-6700, 32GB RAM, Dual 128GB SSD cache and 13TB pool, with SageTVv9, openDCT, Logitech Media Server and Plex Media Server each in Dockers. The main catch here is that the 650 is an IR (infrared) remote, not an RF (radio frequency) remote. My goal was to get my Harmony One to run a FireTV Activity, i.e., turn everything on and switch everything to the correct settings. In worst case, if you have the original remotes for your devices, you can "teach" the 650 to work with the buttons on those remotes.
Logitech appears to regularly update the device database that's used when you configure your Harmony remote. Dunno for sure, but I'm guessing it will.