Base model is to ship them your collection, they add them to a cloud account. You can play from there or download the collection to your own storage. Keeping paying them monthly and they keep the cloud account for streaming and backup.
Then, you can 'sell' your discs on their service. If you buy Tom's CD, they pay Tom something, and add it to your cloud collection and physical collection in their warehouse. (or pay to ship it to you).
Now considering that they're not reripping every copy of Dark Side of the Moon, just checking a box. In essence, one copy of the album could move virtually through hundreds of collections, with nothing more than a couple of dollars changing hands and check boxes clicked, each time it changes hands Murife makes a buck.
Of course the catch is that ther's 400 copies of Dark Side. Yours will probably never be the one 'sold'. Even if they're fair and it's processed based on when added, it could be years before they get around to yours. A little pyramid scheme going on? And pricing for buying is all over the place.