Penon OS849 cable arrived. I read a comment saying it bridges the gap between the m15 and m 20 modules (for U18), and a professional review that said it's on par with full silver cables.
It's pretty rubbish, actually. Doesn't sound like a silver cable at all. It's actually less detailed and more blurry than a pentaconn terminated 64 audio stock cable (OSC copper). Warm, chubby -- pretty big detail loss and soundstage shrinkage for the U18. There are other things off with it too, like the ergonomics, and smell.
(Got that factory burnt rubber odor)
I don't regret buying it or anything. Wasn't all that expensive, but yeah -- if you're strapped for cash and not up for experimenting, take this as a down-vote. Especially for using with the U18.