Xfinity Beta Stream App

I was curious if there is a way to enhance my streaming experience through my Roku stick? My internet download speed is very fast (70+ MBPS), yet there seems to be a slight lag when I'm using the Xfinity Beta Stream App through Roku compared to my set top box. I would rent another box, but I do not have a coaxial line on the wall my living room tv is mounted, so my only option is to stream live TV. I am not happy with the quality though, especially when watching sports. Any suggestions? Would a cable signal amplifier help? Any help would be appreciated!