I have my ezcast plugged into my Yamaha receiver to have surround sound, and the router I have is a linksys e2500 dual band. I have most stuff connected through the 5ghz channel, leaving the 2ghz dedicated to guest and ezcast or any other devices. Both bands are on wireless N only, and it's not pointed toward the wall or on the floor, it's sitting on top of my tv stand. My router is fine I have no issues with the roku 2 xs, just the ezcast is always buffering on 720p when streaming from youtube, and 1080p as well. I have the latest firmware and the app update as well. Any more suggestion?
Update routers firmware.
Experiment with router position - should not be too close to wall/floor or other high density objects.
Be sure you use 40MHz channel width and experiment with different wireless channels.
cheap signal booster example, it'll be hard to direct it between floors
Alternatively just forget about it.