Which of my components has the better built in DAC?

The one that sounds better to YOU.

• USB:

  Offers the best potential for high-resolution audio transmission and is often considered the most versatile option. 

• Coaxial:

  A good choice for reliable digital signal transfer, especially if your DAC has a high-quality coaxial input. 

• Optical (Toslink):

  May be suitable for basic setups but may not support the highest sample rates compared to other options. 

There is no 'the best' DAC. There different chips and different output filters. Thus they all sound different. Pick the one you like. ESS chips tend to be brighter, AKM softer sounding, R2R - depends on manufacturer. Use USB.

My Dad has a MA8950 with the DA2 DAC and it really is a great sounding DAC module.   I think you would have to spend $$$ to better it.  It's that good.  

Coax is usually better than Tos because the quality of optical depends on the Tos jacks on the source and the DAC .    

If you read some threads on the DA2 card you'll see that people have spent a good amount on a DAC to find that it's splitting hairs.   

Plug the Node in via a good Coax and you're off to a good start.  Enjoy

Too many believe misguidedly that the only governing secret to a good DAC lies only in choosing a flavour-of-the-month “high-end” converter chip.(…. the worst approach are those floated in the YouTube reviews …especially those touting that this approach somehow elevates cheap build models to “high-end” performance strata ….HINT: they don’t ….)

Think more important, in that the essence of high-end audio musicality also resides in the line signal processing stages, the power supplies (transformers, filtering, regulation), the digital signal processing before conversion, the quality of the key components: clocks, transistors, capacitors, etc.

TAKEAWAY:

Without prejudice to intuitively first using your ears to get a first hint in an A-B direct bakeoff, go pop the hood and check out the DAC design, it’s boards layout, separate linear power supplies, segregation and proper shielding isolation for input and outputs, and the components build quality, for some further clues.
You invariably get what you pay for.