The datasheet is a bit confusing, but from what I gather, pins 7,8 are connected to the resistor chain. On the chip responsible for the upper range, call it U1, connect U1.pin 7 to U1.pin 6(which is the internally generated 3.75V reference source). Then for the chip responsible for the lower range, U2, connect U1.pin 8 to U2.pin7, and U2.pin8 to ground.
This approach won't work for the logarithmic version(AA6878) of the chip - you'll need to add an extra resistor paralleling the lower range chip. The reason I bring up the log is that typically log indicators are used for audio indicators.