Playback from Windows 10 using all 5.1 speakers?

I use Squeezelite-X for playback on my main desktop PC. I was wondering whether there was any way of sending audio to all of the surround speakers, rather than just the front two? My speakers are Cambridge Soundworks DTT2200. I use the onboard Realtek sound on my B450 Aorus Elite motherboard (which has separate outputs for front/rear/centre-sub).
My Onkyo AV amp in the lounge has a setting which "upscales" 2-channel stereo into a 5.1 setup, and I really enjoy listening to music that way.