I have some experience with their premium / stock cables for the A18 - so I'll add in my experience.
I received the standard stock cable with my A18. When I contacted them, they indicated the premium cable comes with the U18 - and the standard cable comes with the A18. That said they graciously sent me the premium cable, and let me keep the standard cable, due to some specifics of my situation. Both were 3.5 mm.
Later, I purchased another premium cable with a 4.4 mm pentaconn. So I have two premium and one standard.
Honestly, the cables themselves (the premium vs standard A18 cable) - look exactly the same - outside of the termination. They also sound the same to me - though that doesn't mean they aren't different - but if I had my guess, they upgraded the standard cable with both the A18 and A12. I also can hear the difference between these cables and other cables. These cables sound better to me with the A18 than the ALO Ref 8 with every DAP I've tried, regardless of module, as the ALO Ref 8 sounds too bright (of course that's not to say that the Ref 8 isn't good, it just pairs better with a warmer IEM like my UE 18 to me - YMMV).
In regards to recessed sockets, there wasn't an option for that on the order page, however my CIEMs had recessed sockets - which is what I wanted anyway.
Incidentally - after extensive DAP hunting and tweaking I am using A18 w/M20 module > 64 Audio Premium Cable > AK SP1000. I also really like the A18 with the Ibasso DX200 - with the m15 module. I'm pretty much reserving the SP1000 for my A18 and using the DX200 with AMP 4 and (trans)portable headphones (i.e. Audeze Sine, MrSpeakers Aeon, LCD XC). with the 6 volt Amp 4 - I finally have a portable that can drive all these planars to their full potential - if I can't be tethered to a desk.
Also,
@twister6 - any cable recommendations that sound similar to the 64 Audio premium, but better? Not trying to tilt the sound further warm/bright - just would like something else that is balanced 2.5 mm is more durable, and has the same sound signature as the 64 Audio cables.