Pros: Great Tuning--These Are Fun To Listen To, Good Detail In the Midrange And Treble
Cons: Incoherency Between The Drivers Is Noticeable, Harsh treble with best detailed filter, detail loss with others, High price, Reliability is a concern
Short Review: All observations made with the high pass filters. Naturally I listened with each of the three filters, but the high pass was my preference.
I really liked the tuning of these. With the K3003, you get an approximation of a neutral sound in terms of a good balance between treble, midrange and bass and the filter system gives you a means of adjusting this balance (at a cost of slightly loss of detail with the non-reference filters). What's great is that the sound is still very fun. I'm not sure I can put my finger on exactly why, but these were great to listen to. I think the combination of the brightness of the treble with the full bass give the fun of a more v-shaped sound, but I didn't find the midrange recessed. Add that to the nice detail in the midrange and treble, and you've got a tuning that lets you sit up an really listen to your music while still rocking out.
The main issue for me was the incoherency between the drivers. You can certainly tell the difference between the sound characteristics of the dynamic driver for the bass and the balanced armature drivers for the midrange and treble. I'm not sure why AKG used this particular dynamic driver, but it's markedly less detailed and has a slower decay than the armatures. It's not terrible, but it's a serious flaw in an earphone with a huge pricetag. I often listen to music where the bass, midrange and treble are equally balanced, string quartets are an example. Another is renaissance polyphony where the bass, tenor, alto and soprano singers must be balanced. The bass voices were less detailed and crisp than the sopranos with the k3003. I imagine there will be music where this issue is less noticeable, but if you listen, you'll hear the discontinuity in the earphone.
EDIT: After writing the review, I've come across a graph which may help: The CSD graph in this post perfectly sums up the issue with the k3003. You can see very clearly that the decay in the bass from the dynamic driver is way, way, way longer than in the rest of the frequency range as produced by the armature drivers.
The treble will definitely be a bit harsh for some using the high pass filters, but using the other filters takes a bit away from the detail resolution. It's a trade off that I don't want to make at $1,400.
Some found issues with isolation, I thought it was average. Others have reported fit issues, I didn't have any, but certainly it's always possible and one can carefully try different brands of eartips. The standard tips worked for me so I didn't explore that.
Reliability is a serious concern as well. The stress relief on the pair I used for this review was showing signs of wear after only a few months.