Heyy Buddy,
Thanks for considering Eletech in your upgrade cables path!
Whilst the synergy matters, it would ultimately boils down to which areas you would like to hear improvements on , your sound signature preferences as well as music you listen to.
Meanwhile, theoretically the Socrates should make for a rather good pair-up with the U18t though i have not yet try that specific pairing before. The Socrates should add in a rather good sense of layering, dynamism as well as soundstage airness. It should be a rather clean setup inching slightly towards a little warmth. Again, i've not tried out this specific pairing so it'll be good if you get to audition the pairing. Let me know your thoughts when you get a chance to!
Here's my thoughts (based off memory) on the "Plato" and "Iliad". I remember testing out this pairing a good number of months back when audio shows was still rampant
; Unfortunately back then "Socrates" wasn't released yet so i didn't have it with me to test it out. In my books, the Plato is a definite better synergy with the U18t as opposed to the Iliad. The Plato opens up the U18t significantly bringing about a perfect harmony of all the details that the U18t churns out whilst adding in plenty of air in the head room. The imaging is much more precise and image are pin-point accurate. Mids are more coherent and full bodied with that set up.
The Iliad whilst adding on a hue of nice warmth, did not achieve as much as the Plato did in the pairing. "Iliad" also added a mid bass texture that i find deviates from the originality of the U18t - thus that pair up wasn't much to my liking.
Hope it helps! Do note that these are based off my personal preferences so it'll be nice if you could listen to those pairing yourself. Would love to hear your thoughts!