FX2LP can be used as USB 2.0 peripheral controller for an audio device. In case you need to have both speaker output and mic input, it would be advisable to have two separate FX2LP ICs. This is because FX2LP has only a single slave FIFO/ GPIF interface and can provide a single clock input/output along with the data pins.
Alternatively, you can use the FX2LP's I2C interface with an external converter to interface with the speaker or microphone. This would allow you to use the slave FIFO/ GPIF interface for one function and the I2C interface for the other.
As a reference prototype, you can refer to the below code example but please note that this is not a complete firmware solution.