If you can't hear the WAV channel, all your other channels are too loud. Turn them down ON THE GAMEBOY before recording or any other sort of post processing. Only after it sounds well on the GB you should pass it over.
Making everything as loud as possible is usually a bad habit.
This is exfremy important. Rarely do I make an instrument on the pulse or noise channels that is above a 9x with the E command. Gotta make that wav channel stand out, not hide behind an explosion of noise n square wave arps!!