Hi
the upgrade is if you have a doser 1 or 2 or 3 and you want to add an extra pump or more to your existing unit, all models can be extended.
here is the direct link to the doser page, scroll down past the upgrade kit to see the dosers and select what version you require.
http://www.progressivereef.com/ghl-dosing.php
SA = stand alone - has built in dosing controller
Slave = model that works only with ProfiLux computer controllers and in doing so has more functionality.