Should I add a DDC?

Yes it would likely make a noticeable improvement.  I added a Hermes into my setup (I have the same DAC) and it made the soundstage wider and deeper, improved imaging and transients.  The Iris will likely make similar improvements.  The Hermes has a much better clock though.  I use the I2S connection from the DDC to the DAC.  So USB to DDC and I2S from DDC to DAC.

Thank you @jastralfu! Very helpful. Appreciate the detailed reply, especially as a Pontus owner. 

Can only mirror jastralfu’s observations.

I added an Iris to my Ares 12th-1, which I then replaced with the Pontus 15th; more of the same but with the uplift from upgrading to the Pontus

Good luck, let us know how you get on if you decide to pull the trigger 👍😊