I suspect you're not yet set up correctly on that DD-WRT router. If you have it set up as a client, then it should pretend that it's wireless side is the WAN, and get it's WAN IP, gateway, and DNS from your main router. I gather that works. But then, as a client, it would normally be set with a different LAN address range, and have it's DHCP daemon enabled to give out it's own addresses to it's wired clients, such as your Xbox and 722. Is that how you set it up? If you entered the same address range on the DD-WRT router as exists on your main router, you are probably confusing it horribly.
One easy way around this nonsense is to set the DD-WRT into bridge mode. I don't have this software running anywhere, but I presume it has such a mode. In that case, it would go nearly transparent on you, and all it's wired clients would get their IP info from your main router and not the secondary router. If that's how it was set up before, that might explain why you couldn't get control of it without a reset to factory defaults.