Hi,

The order in which you connect the PAB devices (KHD, SA Doser (converted to Slave mode), etc.) does not matter. What is most important is that you do not create a loop. For example, you can have a PAB chain like this:
P4e PAB port --> Powerbar-6E --> Doser --> KHD
OR
P4e PAB port ---> KHD ---> Doser --> Powerbar-6E

If you have more than one dosing unit, any additional unit must have the pump head numbering assigned. We have instructions on how to do that here:
https://www.aquariumcomputer.com/knowledge-base/how-to-assign-pab-devices/