I have had my testing unit for two weeks now and I really enjoyed it. I know that you strive to avoid comparison K3003 to custom IEMs on the price/quality level. But as a owner of similarly constructed hybrid UM Merlin I can't help but compare those two.
Firstly, I got perfect fit with standard M tips, so I didn't have to use some aftermarket tips. That said isolation is good but of course customs does better.
As for sound, well... having owned UM Merlin for few months K3003 didn't wow me at first. But that doesn't mean AKG sounds bad or anything. Actually given the fact that these sound on par with UM Merlin makes K3003 the best universals I've heard.
Reference sound filters really suited my taste as for all-rounder. I listen to wide range of genre music from electronica, pop and fems to hardcore and metal. Within all genre K3003 did outstanding job placing each instrument right into its place. I was amazed by the separation. Each sound came from different driver yet the sound's coherency is among the best.
Bass is quite tight, fast but doesn't lack rumble or dynamics. The lowest bass notes lack some extension next to Merlin, but overall they are very good for universals nonetheless. I liked that K3003's bass is always controlled. There's no midrange bleed. Double bass stings performed top notch.
Mids are very detailed, yet airy, soft and light in weight. I found mids to be in perfect spot between being colored or sweet and bight or lifeless. Bottom line the mids were exactly as I like my mids to be. As for universals it's also amazing how AKG manages to change its presentation with song. It's close and intimate when called for and spacious when given some heavy rock tracks.
With some players like HM-601 or Studio-V vocals could turn sibilant at times, however with clip+ or iriver imp-550 cd player sibilance wasn't an issue at all. In fact those two players were able to push the AKG to its finest. I particularly consider AKG K3003 and IMP-550 to be my new (quasi?) portable reference.
Highs are really good with slightly warm sources and a bit metalic with HifiMan od HSA players. I really liked the extension of the highs. It's extremely good and was giving my Merlin good run for its money. When switched back to Merlin I felt like I lost some sparkle to my music. High hats and crashes are always present on K3003 and it makes listening to jazz pleasing experience.
Soundstage is really good. It's spacious, airy and detailed. I feel like there're only few earphones that could match that spaciousness. Holography and imaging is also top notch. There's enough depth to the sound, and some of sounds can be placed way beyond ear and head either vertically or horizontally.
I actually liked all filters. Each has something to it. Bass filters add some more rumble and extension to bass and midbass, making it more present in every track. Vocals indeed went a little bit back and recessed. Mids felt a bit darker. Though I still heard good clarity and separation within mid range. I won't call those inferior to the reference filters - just different. Highs got tamed and I liked it for bright players to give nice synergy with black filters. The earlier almost-sibilant notes were gone for good.
As for high boost filters - I liked the way the mids stood up (more concert alike type of presentation) and the fact that treble filters don't sacrifice highs' quality. White filters make highs a little more extended at the very high end, without adding to hot vocal notes. As for bass and lose of its dynamics, well the bass is for sure lacking punch and wight with highs boost next to the other, however I found listening to Pendulum or some dubstep heavy bass tracks still enjoyable. Bass felt just tighter and less forward.
As for UM Merlin vs. AKG K3003, to me Merlin sounds like combination of different AKG's filters in different ranges. That said it would be like bass taken from reference filters, mids from highs boost and highs from bass boost. Basically Merlin offers quite similar signature as K3003 with slightly different presentation but with matching quality, quantity and so one.
Taking all into account IMHO the AKGs are well worth the price. They are the first earphones I had in my hands (ok I didn't had a chance to use FADs) that offer more than just a sound. It's more like using a quality brand watch or supersports car. The packaging, the leather, brushed stainless steel is quite an experience that engage all the senses not only hearing. K3003 are also the first universals that made me truly listen to music not to my gear. The same thing does Merlin, but then again, AKG are universals.
PS: there's also full review coming in polish, I'll update you soon
Edited by piotrus-g - 7/31/12 at 12:29pm