Streaming DAC recommendation

@audiobuddy there are few different options here. You have streamers and music servers with a built in DAC such as Auralic Altair, Lumin D2, Aurender A200. This category units usually would have their own UI. Auralic’s Lightning DS, Lumin’s UI app and Aurender’s Conductor app (not Roon ready).
Then you have DACs with an onboard network renderer such as PS Audio DSD, Bricasti, and the above mentioned Gustard. These are going to be Roon ready or compatible with apps such as Mconnect. Digital to analog conversion will be the primary focus of these units, with the network renderer being good enough but not on par with a dedicated streamer in $3,000-$4,000+ range. 
 

If you want a one unit integrated solution and are not looking to have flexibility to upgrade the streamer alone, then the streamer/music server with a built in DAC is what you need. If you don’t need Roon, go with Aurender (although there are constant rumors about future Roon integration/certification). Other than that, Lumin or Auralic are good units. 

Lumin D2 is a streamer first, DAC second kind of approach. It’s an integrated one box. 

Lumin, Auralic and Aurender all have AirPlay. These are the established brands. You also have new kids on the block such as Eversolo or HiFi Rose. I haven’t heard either.
There are differences in design between the streamers that affect sound quality. Do a bit of research. Don’t rush. 

@audiobuddy if you’re using a fanless Mac Mini purely as a Roon core and not running it as a streamer or a household computer, it’s more than adequate to serve as Roon core. 
Aurender, as it’s been said above, is not Roon ready. If you’re planning to use Roon, I highly recommend a used Lumin U2 or U1 streamers (not the mini versions of those though).  Auralic is a good streamer but sounds best with its UI without Roon. That puts you at around $3k. Add a DAC like the Cord Qutest if you don’t require XLRs. If you need XLR connectivity, PS Audio DSD DAC can be had around $2k now. That will keep you in your budget and will be a kick ass digital front end.