Well, after careful consideration and one week of extensive testing, I've decided to return my P1s. They're probably the
best IEMs I've come across that I decided
not to keep, and for the most part I think they're worthy of their flagship status. Packaging, build quality and accessories are nothing short of amazing. And as far as sound quality is concerned, let's just say I liked at least 90% of what I heard.
However, I can't help but being rather picky when it comes to realistic timbre of instruments and overall tonal balance. So, in case anyone's interested, here are two things I didn't like about the P1s and which ultimately led to my decision.
Bass tuning:
Contrary to many other dynamic driver based IEMs, the P1's bass is overall well-controlled and not overpowering, which is a good thing. However, the distribution of bass energy across the low range is far from linear to my ears, with its main emphasis in the mid/upper bass region and a distinct roll-off in deep bass.
This isn't quite a big deal as long as bass is just part of the rhythm section, and even provides a good kick without making the sound overly bassy. But whenever bass is played as a lead instrument and tackles its lowest range, the downside of such tuning becomes obvious. Here's an example, listen to the short bass solo starting at 2:35, which ends at 2:45 with a down-slide to about 50Hz. While this effect sounds awesome on IEMs with good bass extension, only the first half of the slide is actually audible on my P1, followed by a quick fade-out at around 100Hz:
Bass vs. treble note-weight:
While bass on the P1 has its main emphasis in the 100-200Hz region that defines punch, the lower treble range is a little laid-back as compared to the higher range around (and above) 10kHz. As a consequence, bass and drums have pretty substantial note-weight, whereas high-range instruments like cymbals tend to sound light and airy. This kind of tuning is actually pretty clever, as it creates the illusion of an IEM that packs a good punch on the one hand, but can still sound very detailed and subtle on the other hand. However, there's no such thing as a free lunch, and in case of the P1, the downside is a disparity in note-weight between bass and treble.
Here's an example, listen to bass and cymbals from 2:00 to around 3:00, the former sounds weighty, almost fat, while the latter sound light and thinnish in comparison, at times almost as if struck with pencils instead of sticks. When listening to the same track on phones with more consistent note-weight, the P1's disparity is easily discernible.
On a final note, I'm aware that we all have different tastes and priorities when it comes to sound quality, and I'm sure some things I'm picky about don't bother others in the slightest. The P1 were ultimately not what I'm looking for, but they're still darn good IEMs... and as always, ymmv.