If a game's music gets repetitive, I just replace the music files with my own. (When possible)
When I play, I prefer to be able to hear sounds. Sounds often help in gameplay. Eg. Shooters, hearing footsteps, knowing where shots came from by sound. Guild Wars, every skill makes a different sound, you'll recognize the more common ones easily. Other MMOs, alerts and such to let you know something happened. (Someone came online, sent you a message, etc.)