I have Samsung HW-Q80r soundbar with optional rear speaker kit SWA-9000s.
The rear speakers were having pretty very low volume in Surround, Adaptive modes (which I mostly use for 5.1 contents). It doesnt seems that rear speakers are week, they can play quite a huge sound but it was somehow lowered from main bar.
Recently, I have updated firmware to latest 1012.6 version which was released in Nov-2020. After that to my and many other owners surprise, the rear speaker volume was even much lower than before.
As confirmed by users of HW-Q90r community, they have huge volume improvement in the rear speakers after updating the firmware to 1012.6 but for HW-Q80r there is no improvement rather we see deterioration in rear sound volume.
The following is my software versions after firmware update to HW-Q80R:
Samsung, kindly improve the rear software for HW-Q80r soundbar also as it was improved for HW-Q90r. It's a software tweak for sure. Apart from that, the soundbar is pretty amazing, only rear has to be heard.
This problem is confirmed by many other HW-Q80r users with updated firmware.