The Roon Ready Cambridge 851N is just an output device Roon can use to play to, it’s not a Roon Core. You need a Roon Core and an active subscription to use Roon with your 851N. Read also:
From the above especially the section: What do I do now?
The Cambridge 851N is a Roon Ready device, but it is not a Roon Core. You’ll need to use a Core machine in order to use Roon. Your MacBook should work for you, but if you have any other questions please let us know! I’d also recommend taking a look at our Help Center.