Automating the switch in any circuit using 8051
In the the part datasheet, it appears the playback trigger pin is a digital input pin with an integrated pull-up resistor.  In that case, you should be able to connect a digital output pin of the 8051 directly to the playback trigger pin.  You could use an open-drain output, since the device has an integrated pull-up, but a standard DIO pin should do fine as well.  You will need to drive the pin low to trigger the playback.  you may drive high or leave the pin tri-stated when inactive.