For some when I played again reason static started appearing partway through in-game (but not in mpv), and turns out it was the -c -c:a pcm_s24le option :/. Strange, because I thought I had played with it just fine before.
Anyways, thanks for the volume adjustment. Works great. Unfortunately ffmpeg doesn't support batch that way actually but I found a powershell command to do it:
ls | Where { $_.Extension -eq ".flac" } | ForEach { ffmpeg -i $_.FullName -filter:a "volume=1.33" $_.Name.Replace(".flac", ".wav") }