1. Connect telephone line to VDSL port of W9980 and connect one of your PCs to its LAN port. Ensure DSL light is solid on. 2. Login web interface of W9980....

Upgrade the latest firmware if your W8960N is not running in latest version. When connection drops, ADSL light is still solid on? How about status of Internet light? Can you login its web interface...

On web interface of D7, go to System Tools---Manage Control to enable Remote Management.

@robjg63 Did you try to disable UPNP as Freddy shares? If you want someone from TP-Link to confirm, you'd better report the problem here. http://ticket.tp-link.com/index.php?/Tickets/Submit

As W8961N is a SOHO device, I'm afraid that it may not be able to work stably if you connect so many devices... It doesn't matter that you use an old switch plus another switch or use a new switch.

Any problem with your internet connection? Describe in details.