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

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.)

For Comcast/Xfinity I have been pleased with my Netgear NightHawk modem.

This connects to  Netear Orbi Mesh Router with an optical link to my streaming system. The optical link replaced a 50 foot cat-6 cable which was a rreal improvement.

@pindac 

When doing a major renovation a few years ago I put in flexible plastic conduit with pull strings inside to help future proof the installation.

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.