Roku TV volume way low under Dolby Digital output using soundbar
My issue is that the sound produced by my soundbar is low even when the Roku TV volume is set high.
I'm using a Samsung HW-R550/ZA soundbar connected to the Roku TV over HDMI ARC. It has optional rear speakers but they are disconnected for these tests and the soundbar has been factory reset. My Roku TV is a TCL 65R613, Roku TV 7121X, software version 9.2.6, Build 4132. Settings -> System -> Control other devices (CEC) has both ARC and System audio control enabled.
My System -> Audio settings are as follows: Speakers: off, Menu Volume: High, Audio preferred language: English. I don't vary these settings for the tests below.
I tested every option for the "S/PDIF and ARC" setting as follows. After configuring the setting, I turn the TV volume to 0 and force a system restart. After the restart,I play the same 20-second clip from Netflix and turn the volume up to 25. Then I listen to the sound.
When set to PCM-Stereo, the sound from the soundbar is exactly what I expect. Sounds loud enough.
When set to Dolby Digital or Dolby Digital, DTS, the sound is noticeably lower and I have to go up to 50 or 60 for it to sound acceptable.
When set to Dolby Digital Plus or Dolby Digital Plus, DTS, there is no sound. This is fine; I don't think my soundbar supports these fancy things.
I want to set the soundbar to Dolby Digital Plus because I own the rear speaker kit for my soundbar and I would like 4.1 sound to be produced. But the volume issue needs to be fixed first.