Streamer + DAC or streamer/dac all in one?

I would not think of separates versus an integrated design as automatically providing sound quality benefits. The guaranteed benefit of separates is really the ability to mix-and-match and change things over time.

Streaming audio is still evolving, and fast.
The same with DAC technology.
For me, buying separates allows me to upgrade in the future-though many good companies will offer upgrades to their products.
One very good buy for a streamer/dac combo is the Bluesound Node. It also has the ability for the user to add a separate DAC, so you get the best of both worlds at a reasonable cost.
Bob

Gdnrbob, the Blue Sound Node is really a great starter dac/streamer it is not a great dac nor a great streamer it is a good piece for its price range.

The higher end dac/streamers are a huge step up in performance over the Node, these units are going to cost $1-2k ish in price. 

The Lumin D2 has the ability to act as a transport as it has a digital output as well.  

Dave and Troy
Audio Doctor NJ Lumin and Blue Sound dealers

I will second @audiotroy 's first post, the one that says, " the best bang for your buck will be a streamer/dac." (I haven't heard personally the gear mentioned in his second.) In theory at least, fewer boxes, fewer cables, less potential for jitter. I used to say, "Make sure it does gapless," but I think that the era of streamers that don't is past us now, thank goodness.

As to changes in technology making the streamer obsolete, I don't think that DLNA/UPnP, BluOS, or even Roon are going away any time soon.