@tmm1 I tried that, but nothing happens (no app is opened) in that scenario.
Whatever you're doing with the Channels Remapper is doing what it's supposed to do and successfully intercepting the command, but is only does so with the TiVo Stream remote. Do you think it has anything to do with the TiVo Stream remote being Bluetooth vs. FLIRC receiving a KEYCODE_TV remote code over IR? 
The TiVo remote doesn't use KEYCODE_TV, they invented some new code (5124) and hardwired it into their OS.
I could wire up KEYCODE_LAST_CHANNEL as a global live tv button, but you can't map that to flirc without a patched Android.
Can you try mapping FLIRC to send F1, then configure the app under General > Remote Shortcuts to use F1 for Live TV?
@tmm1 I don't see "General > Remote Shortcuts" in the App. I'm using Channels DVR 2.1.25 for Android TV, and I see the following within the App:
Settings
None of these make any reference to "General" or "Remote Shortcuts" that I can find.
Also, in Android TV Settings > Device Preferences > Accessibility > Channels Button Detector (currently "On"), there's an option that says "Configuration" but clicking that opens the Channels DVR app to the last screen it was on, but no settings appear.
Am I missing something?
OK, looking up the version number made me wonder whether I had the latest version. Sure enough, Channels DVR 2.1.26 was available on the Play Store. I ran the update, and while I still can't find a settings section for "General" > "Remote Shortcuts" in the updated app, I decided to try re-mapping the Live TV button to KEYCODE_TV and trying the process again.
Sure enough, it worked this time. Live Channels still fired up like before, but Channels DVR live view opened up right after. So then I was able to disable Live Channels and problem is solved.
The "Configuration" within Channels Button Detector still leads nowhere, but that's less of an issue given the Live TV button is intercepted by Channels, as was my original goal.
Thanks for your support @tmm1-- I am new to Channels, and the involvement and responsivity of your team (along with your thoughtful features/integrations) has really sold me on the product. 
Sorry, the settings I was referring to are only in the new beta: BETA: Channels 3.0 for Android and Android TV
Thanks for clarifying. I'll opt in to the Channels 3.0 Beta for Android TV!