Bluesound is the typical entry point. I would recommend Cambridge Audio CXN 60, for roughly $1100. Sounds great (it also has a good DAC, but you can bypass it and use your own). You can play Tidal and Qobuz directly through Ethernet or WiFi. It does Apple AirPlay and Google Chromecast, so you can play anything from an Apple or Android device. It is really good with Internet Radio. The app works well on either Apple or Android. Customer service is quick and responsive, not that you will need them very much.
Cat 5 is sufficient. You may get very slight uptick n sound with higher but not enough to justify rewiring the house.