Hi Peter,
First off all, thank you for using our Edocman extension. Regarding to your question, i would like to answer as below:
As you describer, we think you have 2 Joomla user groups are: Member and Board with 2 different Edocman Categories: Members and Boards.
And you want user in group Member can only able to download documents of category Members, user in group Board can only able to download downloads documents of category Boards.
To solve this problem, you can go to Back-end > Edocman > Manage Categories > Open Category "Members" and click on tab: Permission. Find the group "Member" and allow Download permission for this group, find group "Board" and deny Download pemission for this group. Click save it.
And then, open Category "Boards", click on tab Permission, find the group "Board" and allow Download permission for this group, find group "Member" and deny Download pemission for this group. Click save it.
After that, go to front-end and test the system again to see if the problem is solved.
Good luck
Dam