This mod gives each subclass of each weapon (pistol, rifle, and heavy) their own unique sounds. That way, the Heavy Plasma uses a different sound from the Plasma Pistol, and so on. I did this by using different sounds from both the 1.0 and 1.4 versions of the game. Therefore the original soundscape is not compromised.
It's a ruleset mod, so just enable it in the Mods list.
I'll upload this shortly with a demonstration. Soon I'll update this for the various launchers as well.
EDIT: Updated! Now the Plasma Pistol uses the Amiga plasma sound, and the old Plasma Pistol and Rifle sounds have been moved up to Rifle and Heavy, respectively.
Also updated the Laser Pistol sound with a slightly-higher-quality version (also from the Amiga version)