I've also found another thing that might help the V6 sound quality. In my LG TV's Sound Settings screen, I found that by setting 'Dolby Atmos' to ON and 'Adaptive Sound Control' also to ON, it greatly improves the quality of the sound by making the vocals a bit richer and louder without increasing the background stuff. Hope this helps.
I'm also having this problem too. I've tried everything but to no avail. I'm also experiencing issues with channels now saying that they are not part of my package amongst other things.... Once my contract is over TV and Phone will be gone! Stick to Freeview and On Demand. Sorry Virgin
Virgin refuse to acknowledge its their box/software. No matter what setting I use on my LG OLED55C6V the volume is miles lower than the TVs tuner or other HDMI devices, and BBC1 SD (South East) is significantly higher volume than BBC1 HD (London) - again not on the TVs own tuner. So I get the volume issue when I first change to Virgin on the HDMI, and then again once I've adjusted the tv volume when I switch between BBC 1 SD and BBC1 HD.
In short, it's flaming annoying and just incompetent of Virgin not to have fixed this by now...I have even used another LG TV (2019 model) and it is still the same result.
I have 2 LG Oleds (B7 and B8) and 2 V6 boxes and the sound is poor. I have to turn the volume way up to hear anything and I have to be very careful when I switch to another source as the volume can be very overpowering. I have set the V6 boxes to dolby digital and dolby digital to pcm with no discernible difference in volume.
I can't believe this issue is still going on!!! I am getting a new a/v receiver soon, let's see if that makes a difference, buy I doubt it will as I am currently using the same receiver I had when I was with Talktalk, and I didn't have a low sound issue then.