The line out is not 'line level', which IMO should be the standard.
I run all of my source outputs into a surround sound amp that helps compensate for this. The amp remembers settings for each input in use.
Then the TV can be left alone for volume and the surround amp is used for volume adjustment.
It does seem to help level out the sources a little, but I know exactly the problem you are talking about... and it should be a 'standard' getting developed.
I try to look in the specs on any TV I purchase to see if I can determine the output of the audio out jack,s but often it is not easy to find


I do not work here, but the benefits are still awesome
Make your sound your own!