YM2612 Circuit Audio Signal Offset Voltage
The analogue outputs from this chip will have a DC voltage of approximately 50% the DC supply voltages so that the output can produce superimposed AC waveforms without unreasonably clipping.

This is standard for most electronic audio chips and most signal processing chips. You need to connect to an amplifier using a DC block circuit so that the resulting signal is centred around 0 volts: -



The capacitor value would be a few micro farads and the resistor would be about 10 kohm.

If you can provide more details of the Yamaha chip (i.e. a data sheet link) and explain what amplifier you are considering, closer values can be obtained.