How do you assess a DAC?

It is 100% a matter of taste. If you are looking at streamers look at the OS it has #1 priority, will the OS integrate with your desired streaming sources and formats?

In my system I use a streamer with ARC room correction into my Sony Signature DAC, best of both worlds. Room correction can do things a DAC can’t. Audio lab has the 6000N streamer on sale for around $400 but no room correction.

Martin Logan Unison streamer is on sale at $199 and has ARC room correction.

If you want to drop four figures on a streamer/dac Innuos, Aurender and HiFi Rose get a lot of love but no room correction.

There is the possibility the in-built DAC can be bypassed, this will give a opportunity to compare a presentation.

Give the Off Board DAC a chance using all options for a connection a trial.

I find (my tastes only) that SPDIF/Coax has always been my preferred connection for the device in use when comparisons are done between devices and available connections.  

Keep the DAC and streamer separate.  Get a good streamer and then upgrade your DAC when you can.  Just my $0.02 FWIW.