Which of my components has the better built in DAC?

You have the gear, run the experiment. The NODE DAC isn't broken, but it can easily be bested by a standalone DAC. Easily doesn't mean veils lifting and wives noticing.. Improvements will likely be nuanced and subtle, but crucial, in my opinion.

With my standalone R2R, USB from the Node gives the cleanest and smoothest sound. Again, you will have to try. Implementation often dictates topological advantages*. (See: XLR vs RCA)

You have few ways to connect there -

1. RCA out from Node into Mc

2. Coax out from Node to Mc

3. USB out from Node to Mc

4. Toslink out from Node to Mc

Try it all. My suspicion is the Node into C2700 via USB will sound the best with second best option being coax into C2700. I don’t think the DAC in the Node with node’s analog outputs into mcintosh will match the digital connection.
But it’s worth exploring it all. You never know what will sound best to you. 

Your Mac's DAC should sound better to you.  I would try both coax and USB for the connection.  The biggest difference will be using the USB connection clocking will be done by the Mac which may sound better.

The one that sounds best to you was my first thought, but the all in one Node really shouldn’t be able to compete with the Mac. I have a N130 and it’s really good really works well, but I did upgrade the PSU and I ran it into an external DAC fairly quickly. After I purchased it.