I want to replace the router/modem Comcast with a high quality for streaming

If you have access to fiber optic or DSL you could make the switch and stick with the router the provider supplies. I have a secondary mesh network router system that piggybacks via ethernet cable from the main fiber optic router. The only thing on my mesh network is my hi-fi system. All other devices run off the main router.

No major issues but no noticeable improvements. I just have the hi-fi system on its own network separate from everyone's electronic devices. 

@pindac Correct. So from your central model to your primary router you would have the single run. Then split off from there to another router. Each router either dedicated to wi-fi & data and the other to streaming/hi-fi duties. The other thing is that my wife works from home and having a separate wi-fi network for the data usage means less lag when I want to stream music since it's on its own network.