TP Link 8840T - VoIP - cannot use due to Packet Loss??

My home network now has a VoIP ATA adapter. It is the LinkSYS PAP2 which does the job. The interface is not at all friendly, but a little search provides the necessary settings.

My flatmate, the principal user of the phone, told me that there is a lot of delay in the calls. I noticed as well the few times that I made calls. Nevertheless, I assumed the problem was with my ISP, as the QoS (Quality of Service) on the modem router was set to the port on which the VoIP ATA is connected.
Here is the image of my setup:

It seems that the configuration is not made for mainstream users yet. A script with a setup selection - VoIP, gaming, TV etc.. would make life a lot easier.

For example the Wizard could prompt
"Would you like to setup the Quality of Service for certain devices or computers?"
Then choose which name and MAC address, then specify the type of service. The remaining settings like destination port, priority etc should be defined by the Wizard script.

Computers are no longer for technically inclined people. Nor should they continue to be.