Has anyone done this with a Bluesound Vault?

I assume you know this already, but in case you don’t...the files don’t need to reside on the HD of the Vault in order to be played.  As long as your computer and the Vault are on the same network, the Network Player function of the Vault will recognize and play them.  No need to use up the Hard Drive of the Vault.
  If the goal is to clear the HD of the computer, you can transfer the files to a separate HD and the Vaults will still play them

Mahler.. good to know. Thanks. I have been playing these files from a MyCloud HDD, just wanted to keep all files in one place. That's kinda why I bought the Vault but your point is good information.... I am probably slightly OCD with this preference. haha

I get it...however, the BlueOS will treat all your files as if they all are in 1 place.  Or, if you prefer, you can still look them up by which HD (Library) they reside on.
in theory, you can be playing files from an infinite number of HDs, and not be limited to 2 TB storage.
  I am not sure but I think the newest version of the OS will also treat files from streaming services ( I use Qobuz) as if they reside on the Vault as well.  The last time I used it I notice some of my Qobuz files were in there.  Roon has offered this for a while and it is one of it’s big selling features, so I am guessing that Bluesound is trying to do the same.
  I had moved on from Bluesound to Melco in my two channel system but moved the Vault2 to aHT system.  I just enabled the Vault2 to play files from the Melco just a few days ago and I haven’t really played around with it much

I’m about to go through a similar process with the vault and am wondering if a cache of music on my PC hard drive ripped using DB power amp can *simply* be added to the vault with metadata of course. Anyone try this?

Yes, I have done that. I felt it’s better with the files inside vault. You just need to re-index to get all the artwork.