DAC connection preferred?

It depends upon how the I/O is implemented. What works best for one combo might not be best in a different setup.

My DAC connection Preferred is PS Audio DAC BRIDGE II with a cross over Cat 6 cable from my Mac Mini. The Bridge changes everything better and is a must have component going forward for me.

This is strictly my opinion, but I have owned many, many DACs and transports and servers.

In Order:

1. AES/EBU (if available)
2. Coax with BNC connection
3. Coax with RCA
4. ATT Glass Fiber
5. Toslink

(The above list is using a proper cable with the proper terminations and impedances).

I have never owned any gear that had Firewire or the I2S interface or any other proprietary connections. Those are "supposed" to be better.