Help setting up 5.1 surround sound on Windows 11 (not getting rear speakers)

Help setting up 5.1 surround on my racing rig.

I have a Sound Blaster X4 and juat got Logitech z906 speakees. It's all hooked up (using the 3 colored 6-Channel analog plugs) but having problems. All five speakers test just fine using Creative App and using the Logitech built-in speaker test but when testing it on Windows>Configure Speakers NONE of the speakers make sound. I have 5.1 chosen on both Creative App and under Speaker Setup on Windows.

Playing Forza Horizon 5 I get sound from both front speakers (I presume center channel) and subwoofer but no rear speakers. I have Home Theater chosen in audio settings on Forza Horizon 5. Running a YouTube 5.1 test also does not play rear speaker sound.