I am afraid the answer is going to be a no from everyone that responds. You are going to have to find the volume adjustments in the java app itself if there are any in order to adjust the sound to listen to your itunes.
Get yourself an AirPort Express. That way you can play music from iTunes wirelessly over you HiFi using AirTunes, and turn down the (system) sound on your mac to a minimum, while surfing or playing games with annoying sounds. iTunes controls the volume of the music separately from other sounds.