Mhhh, I can't really follow your thoughts.
The controller of the Aquastream can be mounted on the backside of the Aquaero. If you take a look at
this picture you can see a bit of this construction and you will see a small cable. It connects the Aquaero with the Aquastream to supply it with current and to exchange data.
If you want to connect two Aquastreams to the Aquaero you will need two Aquastreams V3.0 and an other connection cable with an additional connector.
The second controller needs to be mounted somewhere else.