control volume of Command bar with remote of connected FireTV 4K

Hello,
I'm a new owner of the Polk Command Bar and I'm quite happy with the sound quality and Alexa support. But I have an issue with controlling volume of my connected FireTV 4K.
My setup is:
- Polk Command bar connected to my XGimi H1 beamer via HDMI (ARC)
- FireTV 4K connected to Comand Bar via HDMI 2 (as adviced on red lable on the back of Command bar)
Seems that XGimi H1 has no CEC on HDMI as the bluetooth remote of the beamer does not controll the volume of the commend bar.
As the FireTV 4K is my only source I would like to use my FireTV remote for controlling FireTV and volume, but the volume +/- of the FireTV remote doesn't do anything. It doesn't change the volume of the FireTV nor the volume of the Command bar.
Is this correct or do I miss any setup?
By the way, does anybody use the Sideclick-Remote to control other funktions of the Command bar, eg. bass, Voice or Alexa action button? Does it accept the Polk IR-codes?