I had a look in the AMT/Unitor control
panel and I can see the MIDI filter, but it is not clear how to map?
You can daisy chain a number of AMT8 units into one big virtual unit. The manual describes how, it comes down to connecting them through the serial port. Note however that the physical inputs are merged together when doing this. So e.g. when chaining two AMT8 units, you get 16 addressable midi outputs, but still have 8 physical inputs.
To route signals from inputs to outputs in this chained AMT8 setup, use the Unitor8 Control software. In the main page, double clock the ATM8 icon. Then double click one of the patches. This will open the patch editor where you can connect inputs to outputs.