All, Firstly, I really don't want to seem like a dumb-dumb - but does the 585v7 even support MAC address filtering by feeding it the addresses through the GUI? I can't find an access control list anywhere. Secondly, I can't open the Firewall config. I'm clearly not allowed to poke, and I'm reprimanded with 'level is protected and not editable'. I'm logged in with Administrator. I know other users are probably there if I check via the CLI, but do I really need to become root just to check that? Again, thanks.
In case anyone looks searching for info, I sorted this myself. MAC filtering is implicit through the 'Allow New Devices' list. I had to set this to 'New stations are not allowed' and manually run the wireless device detection to capture and allow MAC addresses. I'm sure there's a way to enter MAC address via CLI, but, for the moment, this is fine. The extra firewall settings became available when the modem had synced. Simples!