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. 

@bipod72 Am i correct if I read your post, with the interpretation, with the idea that I would be best to have two runs of CAT 6 or above Cable. With one of these being dedicated to the Transfer of Data for the Audio Only.

The main listening area for the long term owned audio system to be set up, is most likely to be an external of the home dedicated space, hence a digital only audio set in the remodelled home.

Would it make sense to run a separate feed again to the external of the home space, or extend an allocated cable run to be used solely for audio? 

I am acquiring all Cable Types for the project as an advance purchase, hence learning of the lengths I will need. 

Depending on how long that audio run is you may want to consider using fiber  optic.  I had a 50 foot run of cat-6 and replaced it with a fibre optic link and it was a definite improvement.  Transceivers and cable where under $150 on  Amazon.

Side benefit of electrical isolation also.

New Investigation for myself. 

Fibre Optic vs CAT for Audio 

Being a Student is a place I like to be 👨‍🎓.

Here's are some links to the products I bought on Amazon.

Media Converter with Transceivers

Fiber Optic Cord

It can be a bit confusing with the terminology (MultiMode Dual LC Fiber, etc.)