Stereo 20W Class D Audio Amplifier - MAX9744 is a slim little board which has a class D amplifier onboard that can drive 2 channels of 4-8 ohm impedance speakers at 20W each. Power it with 5-12VDC using the onboard DC power jack and plug stereo line level into the 3.5mm stereo headphone jack and you are ready. Since it is class D, it is completely cool-running, no heat sinks are required and it's extremely efficient - up to 93% efficiency makes it great for portable or battery powered rigs.
At the heart of the board, there is the MAX9744 amplifier which is very easy to use, but also has both analog and digital volume control capability. Use a single 1KΩ pot (one included) to adjust volume analog-style. Or hook it up to your favorite microcontroller and send I2C commands to set 64-steps of volume amplification.
Stereo 20W Class D Audio Amplifier - MAX9744 has all components needed to fully use MAX9744. The breakout board has polarity protection, jacks and terminal blocks, i2c level shifting and a spot to solder in a volume pot.
https://www.adafruit.com/products/1752