This box can drive eight speakers (3 Watt each) and play sound files independently from eight micro SD cards (MP3 or Wav). An Arduino Nano is programmed to do sequencing, randomise playback, control volume and set equaliser settings. It all runs on a single 9-12V power supply.
Very cheap to build. The biggest cost is all the SD cards.
To send commands out to all eight MP3 players, I'm bit banging 9600 baud serial data out on eight digital pins.