Just use Roon running on your iMac over Ethernet to the ID41 in your 808v6 - no ‘cable’ required other than the Ethernet connection to both devices, this is of course assuming that you have wired Ethernet in both locations.
Re ripping music, just use whatever CD ripper you chose and store files either on the local disk on the iMac, to a separately connected disk local to the iMac or a NAS and then point Roon to the stored files.
Hi Warren, do you have a non-WiFi network connection in both rooms?
If yes, just connect up both iMac and 808v6’s ID41 card.
If not, but your router in is either room:
Connect the iMac or the ID41 card to it, as appropriate.
Then you’ll need to run an Ethernet cable from the router to the other room. If, as you’ve mentioned, you run it outside, make sure it’s of the “external” variety which is waterproof and UV resistant.
If your router is not in either room, you’ll need to run two cables.
Note: For Ethernet cables, I don’t think it’s worth doing anything less than Cat.6 these days. Bare minimum should be 5e.
Strictly you could still run a direct Ethernet cable from iMac to ID41, but that means that you would have to use WiFi for your iMac’s other connectivity; also, you’d then have a more complicated than necessary setup.
I assume that your iMac is already plugged into the router, but perhaps not. So I was thinking that you’d want one cable from iMac to router and another from ID41 to router (irrespective of the rooms they are all in).