I have heard the Phonak's PFE-232 myself before and indeed it is a universal IEM that clearly belongs to top-tier category/class. I don't dare to consider myself as having heard all TOTL customs/univerals out there, but I came from a pretty humble background of having heard/own pretty much most of the very well-regarded TOTL universals available out there, from the Fischer Audio DBA-02, Sony MDR-7550 to ATH's very own CK100Pro and Final Audio Design's FI-BA-SS. I also do have quite abit of personal listening experience in the past in term of JH Audio's JH13/JH16 demos (non-FP versions), Unique Melody's demos such as the Mage/Miracles as well as VisionEars/Compact Monitors Stage series demos.
In my own words, there is nothing in terms of midrange purity/presence that the ATH-CK100's exhibits, that can be found on the PFE-232 at all. This is not a biased statement or anything even though I personally own the CK100's, but if you would like me to draw some comparisons, I would probably liken the PFE-232's sound signature to be more similiar to phones such as TF10/Westone 3, but obviously the refinement in its midrange quality, is far better than the 2 former models and its instrumental separation/soundstage properties are more in-line/under same league as CK100Pro's. In terms of treble response, the PFE-232's shares more similar traits with the CK100Pro, in that it has quite abit of attenuated response for upper-mids/highs region and its texture sounds much more crispier, edgier and sparkly when compared to phones like CK100.
In short, both PFE-232 and the CK100Pro are considerably much more transparent and cleanly-detailed in terms of the clarity dept compared to CK100, although PFE-232 still doesn't have anything alike with the CK100Pro when it comes down purely to the midrange presentation or even in terms of bass response/texture. From my own experience/memory, the PFE-232's does have a much more punchier bass impact/rumble, while CK100Pro does retain the same kind of texture/details and extension in terms of bass, most of AT's BA models do not quite measure up in terms of bass impact/rumble details when compared to most of the other brand maker's competitor models available out there.
While my earlier comment may seemed like the PFE-232 do have an edge in terms of the bass factor over the CK100Pro, having this characteristics/trait is actually considered a double-edged sword for the PFE-232 in my own perspective. Because of this additional bass texture impact/rumble in the lower-end frequenicies, it induces and gives the PFE-232 an overall U-shaped frequency response thus giving the user a presentation of a 'fun signature'. The CK100Pro while doesn't sound quite as fun-sounding an IEM compared to the PFE-232, its FR response does seem to lend itself to sound much more natural-like, with a much more balanced-sounding presentation overall. (which are probably more suitable when it comes down genres like Classicals/Orchestras)
The ATH-CK100, as what FatalethaL had put it earlier in his own words, are definitely a pair of universals that are tuned to be more vocal-centric, when compared to the newer CK100Pro's. It sounds quite abit warmer in terms of signature, and while its treble quality is not quite as cleanly-detailed/extended in terms of extension, it does retain and have quite a fair bit of sparkle/shimmer in its texture that doesn't make it sound as dull/rolled-off when compared to even IEMs that are known for having a pretty lushed midrange signature, such as the SE530/SE535.
Shigzeo from Head-fi has his own review of the CK100 as well on TouchmyApps site, and in his review article he has previously also drawn some comparisons against the Shure's SE530, which IMO has a better overall midrange smoothness/character when compared to the latter SE535/SE535 LTD models.
Long-time CIEM owners such as FatalethaL/Taeyeonie got to hear/demo my own pair of CK100's via a recent Head-fi meet organised just earlier this mth. Trust me when i say CK100's midrange characteristics is quite unlike anything that can be found out there, in terms of TOTL custom offerings available out there. I have read quite abit of overseas impressions from HK audio communities, with some CIEM owners drawing up comparisons with their own JH13Pro/Westone ES5, and the magical qualities of the CK100 still manage to put up a good fight against tough competitor CIEM models as above, when it comes down to strictly female-oriented vocal tracks.
When you see a UM Merlins CIEM owner as well as FitEar C435/JH16's owner getting poisoned by the vocal capabilities of the ATH-CK100, even though this is a universal IEM that have been available since 2008, it isn't hard to realise that AT has some clear winner up their own sleeves, that you will never find a comparable one among all the avail universals out there that's for sure.

