There is no separate music volume control for the 202G player (unlike the 105, 203, & 305 players).  To balance the volume you will need to acquire a mixer with which you can connect the 202G player and microphone, then send the output of the mixer to your audio system/speakers.  You may then control the volume of the microphone(s) and 202G's music independently.

For your singing pleasure, even at home, we recommend that you purchase a mixer for much better results.