First off, u should use WIRED whenever possible, like between ATV and switch.
Then if you sure you have a dual-band Extreme, make it not go auto, when it auto it means is gonna automatically balance-load all your traffic disregarding what type of traffic u got going in there. Your goal is to assign video traffic as high priority against any other WIFI traffic.
Then u gotta check your notebook. My Air says it has dual-band and can only use one band at a time. I have not deal into detail on that.
After WIRED, I'd say your next easy solution if to configure the Extreme for QOS, IF (and that's a big if, I don't have an extreme). Modern WIFI routers made last year or so, except the cheapest have QOS feature.
QOS = allow prioritization of video traffic for example, or simply told, everything that does through ATV is nigh priority.
If none of the easy fix works, then I have a feeling to gotta find that geeky neighbor or cousin and feed him free pizza!