The I2S cable is important. I read a number of posters swear by Tubulus I2S cables. I just got one off of USAudioMart (Concentus) and just put it in and it is immediately apparent (this was used so broken in) how good this cable is. I'd say its contribution is as about as good and as much as the DDC.
DDC Cableing
I have a new Denafrips Gaia DDC expected to arrive in a few days. My understanding is that except for converting the original input type (USB to I2S), the only real change is to clean up the incoming signal.
I plan to use a high-quality cable coming out of the DDC into the DAC (I2s over a DVD-type cable). But what about the quality of the cable from the source into the DDC? Does that have an effect on the final signal at all given the transformation put on the signal by the DDC?
(Is this a Digital or Cables post, the admins can sort that out.)