Based on what everyone have said, I played around with files & sound volumes and found the right setting.

LBA.cfg
At the bottom of the setting screen, there's volume setup section. Change the "MusicVolume: ###" to "MusicVolume: 102". All the other Vol are set to "255" value. It appears that MIDI vol is controlled by the game.

dosboxLBA.conf
At the bottom of the setting screen, there's [autoexec] section. Change the "mixer cdaudio 50:50" to "mixer cdaudio 20:20"

Hope this helps & enhances the game experience.

This thread seems to refer specifically to LBA1, whereas I am having the same trouble with LBA2. The "dosboxLBA2.conf" file lacks the "autoexec" section, so I can't do that. Any suggestions?

GOG switched to using multiple .conf files. Look in the xxx_single.conf or similar. It should be in the same directory.