I currently/recently have the same interest in getting a streamer only to existing dac, coming from the Bluesound. I did a head to head comparison between the Bluesound and a Lumin u2 mini. Every part of me wanted to say, these will be identical or close to identical and it’s not worth the extra cash outlay. But to my chagrin, the Lumin was audibly better in terms of “tonal saturation” (whatever that means. It went from grey and hard to analog color sound), slightly cleaner treble and more open, smooth sound. Basically it decreased digititis almost completely. I believe they are priced at $2400. The app was excellent and IMO superior to Bluesound OS.
I couldn’t stomach the cost at this time however so I am about to try the ifi zen. We will see…
good luck. Check out Lumin if you have the funds. It was really great and left me wishing I could justify the spend.