The β22 Stereo Amplifier If you click on "other options" and go to the bottom you can see how the 6-channel is set up. Basically only 4 boards are actually used to drive a pair of balanced headphones. The extra two boards provide active grounds for TWO pairs of unbalanced headphones. So for single ended headphones its like two full amplifiers in one box. If you only needed one single ended headphone output, looks like you could go with 5 boards instead of 6.