Hello JV06089! You can try performing a hard reset on your soundbar. Once the reset is complete, do not pair the rear speakers that originally came with the HW-Q850D. Instead, pair the SWA-9500S speakers. Please note that only one pair of rear speakers can be paired to the soundbar at a time.
Reset using the soundbar controls:
With the soundbar ON, press and hold the Volume + and Volume − buttons on the soundbar at the same time for at least 5 seconds until “INIT OK” appears on the display, then release.
If that doesn’t work, reset using the remote:
With the soundbar ON, press and hold the SOUND CONTROL (gear icon) button on the remote for about 10 seconds. You will see “150Hz” appear on the display. Continue holding the button until “INIT” appears, then release.
~ Samsung Solutions