Here's my impressions as promised. I received my cable on friday and I've done some extensive Etymotic listening since then.
Comfort/Ergonomics:
This was one of my main reasons for getting the APS cable and it doesn't disappoint. With the new cable, it's incredibly low profile and it stays very well behind the ears. I used to wear the original cable this way too, but it was sticking out too much and I had to replace it behind my ears once in a while. Also, the new cable is stiffer than stock cable and it works as a memory cable which is a good addition. The downside to this is that it's less flexible and it's pretty hard to make it fit in the small Etymotic pouch, but it's not a big deal for me.
Sound:
The first thing I noticed with the new cable is the wider soundstage. Compared to stock cable, it's quite weird to say, but it seems to take more space horizontally and less space vertically. The music is closer to your ears than the inside of your head. Also, it seems like you're closer to the band, though not Grado-style. More like first row of a concert hall.
Another thing I noticed is that the treble lost some of the sparkle that the Etys are known for. It is definitely smoother than stock cable and I think it's a little bit less detailed, but there is still more detail than any other IEM I've tried. Paired with my Mini^3 amp, the Etys sound more laid back and a little bit more "fun" to listen to.
The best feature of this cable, IMO, is the presentation of mids and bass.
I always found that Etys mids were quite cold, but I loved the very fast attack and the ton of micro details. Now, with the APS cable, the details are still there, but it brings a lot of warmth and the vocals are really "in your face". It sounds very natural and it feels like the singer is singing for you.
The bass is bigger than with stock cable and a little bit bigger than ER4P. The tightness is pretty much the same, but it sounds more fat and has better impact. It's still not a basshead phone, but it's a satisfying experience coming from ER4S bass.
Finally, I noticed that the Etys with the new cable sound awesome with classical. I'm listening to the last movement of Mahler's third symphony and it sounds more lush than with the original cable and everything seems to blend together instead of hearing individual parts.
Price/Value:
I agree that 200$ is big bucks for an IEM cable and I was very skeptical that the changes in presentation would be worth it, but I'm very surprised by the differences it brings to the sound. Also, the cable is beautiful and it looks like Alex did put a lot of time do build it. My advice would be to buy it only if you've had enough time with the ER4S to know that it's the right universal IEM for you and you want to enhance the experience.
Here's some eye candy: