From the Roon Partners page, it looks like the Bluesound has been certified as “Roon Ready.” This means that the manufacturer has used the SDK provided by Roon Labs to integrate the product with Roon.
Looking at the back of the MXR-540 receiver, it looks like it has a couple of COAX S/PDIF inputs. The best connection option is to use a 75Ω COAX S/PDIF (RCA) cable between the Node and your receiver. If possible, also use a wired Ethernet connection for the Node.
Once you’ve made these connections, the Node should show up on the Audio tab in Roon’s settings. You can enable it as an Output. Once enabled, you can select the Node zone and play music to it.
There’s no need to connect your MacBook directly to your audio system. You’ll be streaming to it over your home network to the Node.