Hello Tuan,
I find this topic because I have exactly the same problem as Jarek. I explain.
Each user in my Joomla site belongs to a special ACCESS LEVEL. I manage projects and I build a new access level for each new Project. A project is dedicated to some users.
Then I want to give to each Project (= one access level) his document manager. And I try edocman for this purpose. I want to use a generic menu for Upload, a generic menu for Category list, but it is too difficult to manage it. Because the upload menu is linked to a named category, instead of to be linked linked to a chosen category among those available under the Access level. Your architecture seems not to allow this kind of approach, isn't it ?
If there is no solution (what I feel), like Jarek I regret not to be able to try the backend of edocman before buying it.
Have a nice day, Hugues