The Sensor Interface Board has sensor interfaces and signal conditioning for light level, sound level, barometric pressure, ultrasonic motion detection and ultrasonic distance measuring built in.
Notice on the schematic that it has a single Polaroid sonar board with 8 reed relays to drive 8 different sonar transducers. This is just one of the many innovations that we came up with while developing the Gemini robot.
The schematics are available for free on the download page.
This is an unstuffed board which is the only image I have of the Sensor Board.