The avast! SBS Suite contains: avast! Server Edition, avast! Professional Edition and ADNM licenses/products.
If you install avast! Server Edition in your Server, you have to install avast! Professional Edition in your workstations.
When you buy avast! SBS Editon you received a "license.dat" file for the server and a Lincense Key, the same for all your workstations.
So, to install your clients you have to download avast! Professional Edition and install it on them. Then activate the license key.
The procedure changes if you use ADNM.