To increase the volume of a file by 2.0
ffmpeg -i input.wav -filter:a "volume=2.0" output.wav
after input file name if you have more than one sound track in the video.
ffmpeg -i input.wav -map 0 -filter:a "volume=2.0" output.wav
Yes, that should work.
There is a huge set of commands in their wiki. Also there is a wide community support when it comes to ffmpeg.