I have both setups, all in one and separates. The all in one is the Auralic Vega G1 and the separates are a Bryston BDA-3 DAC with the Sonore ultraRendu for streaming. Both are wonderful, but I do prefer the Auralic Vega G1 for its compact design, wonderful screen that shows me the album art work and how simple it is to set up and stream both from my extensive collection of digital files (all types of formats) and streaming services, not to mention all in one box saves on cable expenses that then can go into the equipment. I have both connected via Ethernet and use ROON to manage my streaming; both my digital files and streaming music from streaming services.
The advantage of separates are if one goes on the blink you don't loose both DAC and Streamer, and if you decide you want to upgrade the DAC down the line due to improvements you only spend money on the DAC.
From what I understand the DAC is the most important piece between the two pieces of equipment but the Steamer is also very important so thinking about spending the lion's share on a DAC and then picking up an OK streamer, in my opinion, is not a good road to take. Do not cheap out on the streamer it is important and you won't be able to fully appreciate the DAC if you have a mediocre streamer.
Lastly think about the program you will be managing your files from. Some streamers come with OK programs while others are much better, then there is third party programs such as ROON or JRivers. All this should be considered prior to purchasing.