So, lets try just moving the Roku 3 devices onto AE ...
Now, theoretically, any Roku based interference should only impact the Roku devices themselves.
edit: also, once I transition the Roku 3 boxes to my wired network so am able to turn off wireless, I'll be able to "lock" the WiFi Direct channel per this post:
If you use wireless on the Roku the WiFi direct channel will always be the same. Once you force it to a channel you have to turn wireless off and leave it off. If you turn wireless on for any reason then the WiFi direct will change to the channel being used. I forced my Roku 3 to 5Ghz channel 165 many months ago. I have not touched the wireless on the Roku since then and WiFi direct is still using channel 165.
source: avs forums