My recommendation, after having this router for a year and at first really wanting to believe in it... is to move to either an Apple Airport Extreme (I purchased this after having the 855 for more than 6 months and needing dual-band) or purchase one of the Linksys dual-band routers. I don't prefer Linksys since their support is also pretty bad, and not that I'm an Apple fanboy (let me tell you, far from it) but I can say that the router works. It doesn't have SPI as the Linksys or D-Link, but I'm sure you'll have more luck using it than one of the others.
I used to LOVE Linksys, and switched to D-Link with much hesitation, and regret it substantially. I should have listened to my gut. D-Link tech support is non-existent in my case. In fact, I think they made matters worse than they did to help me.