How do you make a final decision on a DAC

The biggest thing is to be able to demo or at least have an at home trial from one of the online vendors.  I ended up listening to a bunch of different DACs before deciding on the Simaudio Moon 280d.  I wanted something brighter to offset my very warm sounding system and can also function as a high quality streamer.  The Moon fit my requirements and sounded amazing.  

I agree with the above poster that there are really no shortcuts when it comes to digital audio, i.e. DACs.  I went from the DAC in a $168 DAC/Amp to a $99 standalone DAC to a $360 model to a $3500 unit to my current $11,000 DAC and there was an improvement with each step, so you usually get what you pay for.  That being said, I was surprised at how close in sound the $3500 DAC was to the $11,000 unit, so I guess Stereophile was correct when they described the ever-increasing importance of the ever-decreasing difference.  When you think about it, getting what you pay for is really intuitive.  DACs generally have two sections:  digital and analog.  For digital, better processors, filters, power supplies, and other components cost more and sound better.  Same with analog:  larger and better power supplies, circuitry, capacitors, resistors, inductors, and other components cost more.  I have found through auditions and purchases that DACs in the same price range generally sound similar although there are some differences, but they are not great.

I went with a Bricasti M3 largely to save money with its built in streamer.  I also have positive prior experience with the brand's demos, and the resale value is stable. My initial interest was in Totaldac from prior demo experience and Holger Adler's endorsement, but they rarely available used. 

Go to Audio Science Review and look at the test results. Choose a DAC within your budget with the least distortion and best linearity. No magic involved!

FPGA 
Then you can load whatever firmware that sounds the best to you.