Please take your time to read the above linked pages from the official documentation, they should answer these questions.
A Roon Ready device will work and isn’t the same as two Roon (Core) installations. Of course, a reliably working network connection between the core and the zone(s) is a prerequisite for such a use case.
Typically, ethernet is used in conjunction with a device that takes ethernet and converts it to USB and is running the RoonBridge endpoint software. So, Innuos connected to home network via ethernet, anywhere else in the home, ethernet to Ethernet/USB converter to DAC endpoint (there are also Ethernet to Coax converters as well).
Prices of these can vary tremendously as usual. On the cheaper end, you could go with a Raspberry Pi 4, microRendu’s are very popular, or even setting up a small little computer running your OS of choice (Windows, MAC, or Linux) can do the trick.
You connect your new Roon Ready endpoint into your Ethernet network or a very good WiFi signal. Use your remote to go to Settings, Audio and enable the new device. Select your music, pick the new kit as your output and you should be good to go. It really should be that simple assuming your network is sound.