2-3k budget - adding DAC/Server to Bluesound Node?

also would consider using an ipad or macbook air (or even windows/android tablet)

as a server if that might represent a better option

If you only want to listen to Tidal/Amazon, and you already have a Node, buying the Vault doesnt make sense.  The Vault does 3 things: 1) Rips and stores CDs  2) acts as a streamer for services such as Tidal/Amazon, Internet Radio, or the aforementioned ripped CDs  3) is a DAC.

   The Node does 2 and 3.

   In your case I would blow the budget on an external DAC to best the DAC in the Node.  If you later become dissatisfied with the Node as a streamer you can upgrade it, but presumably you must be happy with it since you are considering getting a Vault

Ayre Codex- under $1K used

Schiit Gungnir or Yggy

Ayre QB-9 Twenty-well under $3K used.

Bob

I have used a few different DACs with Vault 2i and each upgrade was.more than subtle.     Eventually I will replace it but the Bluesond streamers can sound really good with a nice DAC

Upgrade your Node first. The Node can be improved by a good margin by upgrading the internal power supply with a PD Creative board - https://pd-cf.com/.../bluesound-node-2-2i-upgrade-low.../

I power this board with a SBooster LPS. Takes the node to a level that you would need to spend $$$ on to achieve. And as others have said, a better DAC will then keep you happy for a long time.