You will need five GPIOs to control you multiplexers. Four for channel selection: S0, S1, S2, S3 and one for the enable pin (/E). You can tie this pins together at every multiplexer, so you will only be able to read the same channel on all of the multiplexers.
Furthermore, you will need six ADC input (analog input) to connect to outputs (Z) of the muliplexers to the Arduino.
The operation is simple.
- Select the first channel on the MUX16s with S0-S3.
- Scan your first MUX16's output.
- Set the S0-2 of the MUX8 to the next channel (next MUX16).
- Repeat until all MUX16s are read.
- Select the next channel on the MUX16s with S0-S3
- Repeat until all channels are read.
Here is the circuit for three multiplexers, you can easily add the remaining three.
Note that, this way you can only select the same channels on the multiplexers. If it is not suitable for you, then you can use more GPIOs.
simulate this circuit – Schematic created using CircuitLab