If your particular 601 router doesn't have additional QoS rules then I would recommended to get a router that does. One of the following routers have the advanced QoS rules: DIR-857, 835, 827, 825, 655, 645 and 628.
Then you can apply those game settings in that sticky and gaming should be good after that.
This 601 is a good router for basic use and for one xbox. Having multiples, you really need a router that can handle multiples and have the ability to effect and control gaming connections.