Dac with separate streamer or Dac with built in network card

I think we can mentally mas... er, theorize, but ultimately the quality of the DAC and output stages and which appeals to your ears matters a lot more. 

I strongly suggest before you rule anything in or out you spend time listening.  The Alpha DAC is (was?) used by Magico to demonstrate their speakers for good reason, even without a USB interface.  

So, I’d go for listening + convenience + good user interface over USB and all in one considerations.  I can't stress enough how important the user interface is and making sure it's compatible with your remote devices (iOS vs. Android).  

I always prefer separates... all things being equal they will sound better... allowing greater isolation. More convenient when you next choose to upgrade... as you will be able to select only one function to upgrade. 

Both Lumin and Aurrender are good choices. I recommend Aurrender... for everything from sound quality, customer support, and interface. I also recommend Berkeley their DACs are great sounding and quality construction.  AES / SPDIF are well established standards and work incredibly well. The Aurrender / Berkeley combo is fantastic, I have had it in my system and highly recommend it. 

It varies wildly from device to device and what streaming software you use.  There are several factors and a lot depends on these factors.  

A major benefit of a DAC with an on-board streaming card that serves as a UPnP or Roon endpoint is that the internal connection is via I2S which has many more wires available to ensure proper clock synchronization via the ribbon cables.  If you look at an I2S pinout there is left and right signals for the audio data and the clocks going in both direction along with appropriate grounds. 

This means that generally speaking, a streaming card, despite not being in an outboard chassis and having a separate PSU has distinct advantages that will make it perform at a higher level than you would expect do the modest incremental cost.  

Particularly with Roon, I am heavily biased toward on-board streamers for this reason and find that the quality of your server is less important with a good endpoint.  There are exceptions to this though where the Roon endpoints are just awful and an external server will be much better.  

That said, not everyone uses Roon.  Few manufacturers have their own software and even fewer have their own software that works.  Secondarily, it is important to look and see if the on-board streaming card has a buffer built in.  For example, Linn buffers the music for 4-5 seconds.  Particularly during the day when internet takes a lot of traffic, you can have momentary bottlenecks on your network that cause dropouts.  Without a buffer, this can be maddening.  It also tends not to sound quite as good as it dow with a server because the flow of data isn't as steady as it could be. 

So...what does this all mean?

The right solution is the pick a DAC that sonically matches your system.  There is no scenario where a Weiss 501/502 and a Meitner MA3i are going to work equally well in the same system.  The Weiss is colder and more analytic while the Meitner is warm and sweet.  This is not good or bad.  If your system is laid back, the Weiss can bring it to life.  If your system is a bit bright, the Meitner can tame it and make it more listenable.  

Once you have selected the DAC based on synergy, I then suggest looking at that unit and picking the best way to connect to it which could include an outboard streamer or server or you might pick a streaming device like the Linn and be done with it.  One thought of course is that if you are prepared to spend $10K+ on a DAC, and $10K+ on a streamer, you might find a $20-$25K streaming DAC will be better.  

A Linn Selekt w/ Dual Mono Organik, Weiss Helios or Rockna Wavedream Reference Signature is going to crush a Weiss 501/502 with an Aurender or that entry level Berkeley with an Aurender.  Linn you can use their software which is brilliant though I find a bit clunky.  Weiss is one of the few devices that is tested and confirmed to work flawlessly with JPlay and the Rockna is INSANELY good via Qobuz Connect.  

Whether you look at the devices I mentioned or something else....start thinking about DAC and system synergy.  That will narrow to a list of units that will make sense based on sonic profile then look at the feature sets and see what fits your budget and needs.  You will end up in a much better place.  

Full disclosure, I am a dealer for Weiss, Rockna and Linn.  I have no association with Berkely or Aurender other than having had used products in on trade.  That said, not even advocating you buy from me.  Just get the process right so you end up in a happy place.  

I think I was one of the folks who suggested you consider the streaming DAC. @verdantaudio put it well, having the streamer in the DAC and using short cables for an I2s connection, as the protocol intended, makes for a very clean implementation with the least amount of manipulation of the stream. It all comes down to implementation of course, the streamer card has to be good, and low noise. And, it more than likely ties you to Roon, though there are options, e.g. JPLAY.

I recently migrated from Innuos/Merason via USB to Antipodes CX/Bricasti M3 connected via a very short direct Ethernet cable. The CX is built specifically to interface this way, with two network connections. I compared virtually every configuration of all this gear, the straight network connection easily bested SPDIF and USB. 

I would like to hear the Meitner, though coming from the warmth of Merason to the forthright, but not bright, presentation of Bricasti has been very enjoyable. Maybe a hair less musical though. I am sold on the streamer DAC. Two others reference level streaming DAC’s to consider are the Tambaqui and the new PS Audio Signature DAC.

i am not sure that I saw the other thread referenced.  What was the theoretical advantage of a DAC with a streamer card in reducing jitter?

  I normally recommend separates for streamers and DACs, but if jitter concerns are that paramount, then perhaps a combo player would be your best choice.

  In the budget range under discussion, you are going to end up with a pretty decent results.  I don’t particularly care for the Weiss home sound but every other brand mentioned here is superb, and you may feel differently about Weiss.