Surround sound not coming through Roku controller

I have a Samsung smart TV which was set up with surround sound a few years ago through a MX-890 universal remote.  I then installed a Roku a couple of years ago but decided to upgrade it to one where I can control the TV ON/OFF and volume through the Roku controller only.  Well, I just connected the new Roku with the HDMI cable and USB power cable and it set up fine and I can turn the TV on and off through it.  However, I am only getting sound from the center speaker using the Roku.  I can still get surround sound using the MX-890 remote.  I checked the audio settings for the Roku and it is set to auto to get the best digital sound.  How can I get the surround sound by controlling the volume on the Roku controller?