I use a Matrix X SPDIF 2 between my Innous Zenith MKII streamer and PS Audio Direct Stream DAC. For I2S, I use a .7 meter Wireworld Platinum Starlight 8 HDMI cable. I get a very noticeable SQ improvement via I2S as opposed to USB from the Zenith directly to the DAC.
I'm sure there are better DDC converters than the Matrix, but I'm quite satisfied with it in my system.