Honestly, I wasn't planning on getting this far into the Network game foolishly thinking that I would get minimal improvements playing locally stored files.
Lucky for me, Comcast has been sucking lately, charge an arm and a leg, and give 1/3 the speed of ATT fiber at 3x the cost. The original plan was to replace Comcast with ATT fiber for the entire house, but now I think I might have to keep both, and use ATT Fiber only for the Extreme/music.
The improvements I've heard are too much to give up now and I don't know how much of that is attributed to keeping all other house internet traffic off of the ATT fiber line. I will test adding the house network to the ATT fiber line to see how much it degrades the sound once the Edgerouter is setup and I use the SFP port to feed the rest of the house.
I too have Att fiber and have made some modest moves to circumnavigate the Att modem/router Gateway:
-- disabled the Gateway wifi
-- connected Home wifi router to modem via fiber and fmc's to isolate Home traffic from Audio line
-- lps to modem
I also thought I would attempt to bypass the Modem with the Edge router as you described a couple of posts above. However when I talked with a Networking professional about setting this up for me, he warned me I would without a doubt be in for some technical troubleshooting and maintenance from time to time by doing so. As I am tech/networking illiterate and value my sanity, I chose to forego that endeavor! But if you are comfortable with this, then go for it!