The Bluesound Vault would be a convenient option, since you already have a Node. I'd probably lean toward a general purpose computer instead. You can get a Mac Mini M2 for less than the price of a Vault, and it will do more. You could set it up as a music server with Roon Core or Audirvana, or simply store downloaded/ripped music files on its hard drive then expose them as a shared Bluesound library to the Node.
Some people favor a dedicated music server (such as Small Green Computer's sonicTransporter, an Aurender, an Auralic Aries, or a Roon Nucleus.) I'm sceptical that these devices deliver any noticeable sound quality improvements. They tend to be much more expensive than a Mac Mini or a NUC, and usually don't support a wide variety of music-related applications (like the HD Tracks music file downloader, Apple Music, or REW). I do have one, though (the sonicTransporter i9,) in addition to a Mac Mini.
You don't necessarily need to buy anything new, if you happen to have an old computer lying around. Whether it's a general purpose computer, an Aurender, a Vault, a NAS, etc., basically what you're doing is setting up a network-accessible storage device to expose your music to one or more networked endpoint device(s) attached to your HiFi system. There are many ways to do this.