Can you please list the changes in the router's configuration have already been tried, also the firmware version on the unit? This would ensure that our suggestions are not redundant. As you've already determined by reading the manual, this unit has a built-in WMM function and you do not need to enable the QoS Engine Rules if you are concerning about maintaining the priority of audio, video and voice applications since enabling the WMM function will provide other applications and traffic to less likely to slow them. If you want to prioritize some of the traffic for your Skype machines, consider enabling the QoS Engine to meet your expectations.