I see that the 605L has different options unlike some of the other DIR series routers. I'm wondering if maybe you might get into a different model router that has some QOS options. I see that the 605L has some Traffic Control options however I have never used this model router and not sure if this would be a good option for use with Gaming on XBL. Any chance of using a different DIR series model router by chance? If your into gaming, I would recommend a different DIR series, I've used a DIR-857, 835, 825, 645, 657, 655. If any one of these are not available to you, list the DIR series model that are besides the 605L and I'll look and see what QoS options are available.
If anything maybe we can use teamviewer and see if we can get up the 605L and see if we can make it work.