@Adimon,
Unfortunately, I am somewhat a DAC harlot
, having several. One of them is the Directstream, which I just recently put back in rack to check out I2S from the K50. I read on their forum the postings from people buying a number of different I2S cables and picked up a closed out Wireworld Starlight 7 a couple years ago. Not having an I2S source then, I also purchased a Matrix X-SPDIF2 to convert USB coming from a microRendu and a Small Green Computer server. I liked that better than USB with several different USB cables.
I have made a number of equipment changes and additions since then. I recently updated to latest firmware for the Directstream and tried this cable with the K50. Audio memory is so very short, but feel this is probably the best I had heard from the Directstream (DS). I have not tried AES/EBU to the DS. I did try AES/EBU with the Mola Mola Makua DAC (very similar to Tambaqui) from the K50 with an inexpensive cable, Mogami W3080 with Neutrik XLRs made up by Redco Audio years ago. I recall trying this cable years ago to Directstream, but not liking what I heard and putting it in storage. There have been many PS Audio firmware changes since then and many equipment system changes since then. I was happily surprised how good it sounded when I recently put in the Makua, and has me wondering if I should evaluate a better cable. If I do, I hope to retain enough sanity to test from companies with a return policy or very good price on preowned. My cable purchasing has been far more modest than my DAC purchases, sourcing quality from less expensive sources like Triode Wire Labs, Audio Sensibility, and a couple WireWorld items.
The Tambaqui has I2S, but Makua DAC does not, so I cannot test I2S cable with it. Running ethernet from K50 outgoing port to the Makua utilizes the Roon Ready player in the DAC, not the player from the K50, while the other digital outputs reflect the Antipodes player. I have noticed some subtle but noticeable differences in the digital output sound signatures from the K50 to Makua, depending on ethernet cables used into and out of the K50.
For the DirectStream, I would guess the I2S from the K50 would be best, and offers you more bandwidth.