Synology NAS units support 6TB disks. WD Reds, Greens and Purples. HGST and Seagate.
I would also believe that Q-NAP and Thecus support 6TB disks.
Those are the three largest SOHO NAS brands.
Thank you very much
When choosing between the three brands I mentioned, each of them have an on-line demo of the user interface. Play with the user interface and see which one you like. If you have specific features you want from a NAS post a new thread and ask for suggestions based on features.