Hi,

You're right, the COMMAND message and in general all updates are sent to all the clients subscribed to the specific item.

Note that you can - starting from a common name client-side - modify users subscriptions server-side:
In the MetadataProvider interface there is a method called getItems. You can implement it to customize the items to be subscribed per each user.

Hope that helps,
Goodbye.

PS: you can also implement the customizeUpdate method to customize each update on an user basis. Btw take count of the advices of the JavaDocs.