Arduino Audio player using TMRpcm and LM386

We are trying to create a very simple music player using the TMRpcm library and an amplifier module similar to this.
We connected pin 11 to the amplifier input and powered the amplifier with a 9V battery. We then played 8bit 16KHz wav files stored on the SD card using the TMRPCM library. Unfortunately, we are barely getting any sound through the 8ohm 0.5W speakers. Does anyone have any experience with a similar setup?