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

Thanks for the coaching @fastfreight .  You're quite a role model. 

@lalitk , +1 on the LinkUp 22g cat 8 cable.  I had initially run Supra cat 8 (my runs are about 40 feet) and the LinkUp is better.  I got this from you a bit ago, thanks!

Reasonable cost also from Amazon.

Hi @carlsbad2 ,  I will retract 'snarky'!  Would love to hear a Lampi DAC like yours in my system.  I see we both share the Grimm.  Have you seen GTT's  internal MU1 modification  with a new Realization ethernet cable?  Bill states it is an easily heard upgrade.  I have done it with another cable (and it is easy to hear), but my KS is coming.  I think any good ethernet cable inside the Grimm vs the generic one is an upgrade.  It plugs in at both ends with a standard ethernet plug, and is either 13" or shorter depending upon the MU1 version.  I have learned that it is THE LAST cable before your streamer that matters the most.  So no matter what cable (or filter) employed prior to the Grimm, the internal stock cable degrades it.

I got a Netgear CM1000 modem to replace my Spectrum supplied modem.  I use Ifi low noise power supplies with both the modem and mesh router.  I didn't hear much of a difference myself but since this modem performs better, ie less dropouts, fewer problems, I kept it.  Plus the modem paid for itself in about a year by dropping my ISP's lease payment for use of their modem.  Ethernet cables, I found make a difference.  I prefer silver plated and also found the best ethernet cable should be at the streamer.    

carlsbad2

... Now the audio system will plug directly into the modem ...

For all kinds of reasons, including security and the ability to set static IP addresses, the only thing I plug into my cable modem is a router. I have Comcast and have used a Netgear CM500 modem for years without issue. With the network configured that way, it’s easy to isolate the source of any speed or stability problem.

My Bryston BDP-3 streamer is hardwired ethernet direct to the router, which is at the far end of the house. It’s amazing how a skilled electrician can snake wires through walls to accommodate that, and I’m convinced that no wi-fi is the equal of a wired network. It’s worth the one-time cost to have it done, and my audio system looks neater without all that computer stuff in the room, imo.

I’m skeptical about products such as the Switch X. But I’ve never tried it so I have to reserve judgment. After all, in a world far away, I once believed cables wouldn’t make a difference.