Dilshan Jayakody has written an article about his open hardware project known as Smart Audio Box (SAB):
Smart Audio Box (SAB) is microprocessor controlled audio switch and amplifier system, which is specifically design for audio composers and for audio engineers. SAB consist of 4 high impedance stereo inputs and two output modes. One output mode can drive stereo headphone/earphone and other output mode can drive pair of 8W speakers. In prototyping stages we identify those modes as “Personal Mode” (headphone output) and “Audience Mode” (power amplifier output).