Great review. I have the K3003's and T1's and enjoy them both very much. I am having serious issues with the cabling on the K3003's though; the shroud has come away at the earpiece revealing bare wire. Am trying fixes, but it really worries me, one snag and they'll be toast

Lovely review, though I'm curious about your comment in the IE800 section about all Sennheiser headphones being 'warm sounding and easy to listen to'—are you including HD800 in this category?

Enjoyed your review of these IEMs - although I did not think they were as good as the IE800s. The IE800s have more detail and a warmer sound and a wider presentation. This is the bit I got stuck with. "The soundstage is also very large in this IEM, but not as large as the K3003i." The 3003i's have a more energetic feel to them than the IE800s. The IE800s sound more refined and more spacious

Let me clarify - I preferred the IE800s over the K3003is. The AKGs are a more accurate representation of the music to me. The IE800 is a more artificial one. The IE800 sounds more refined the 3003 more lively 

@salla45 I know that AKG will repair/sell replacement cables.  If anyone can create a detachable cable solution, that would be awesome!

@bosiemoncrieff The HD800 is definitely not warm sounding, but almost all the other Sennheiser headphones and IEMs I listened to are.  I feel that the HD800 is designed to be more neutral so as to sound more reference and are a departure from other Sennheisers in this regard.  When I have the perfectly recorded file playing through my CMA800R > HD800, then these headphones sound pretty amazing with the widest soundstage and the best dynamic range and detail retrieval.  The problem is, this is something that happens rarely, and I suspect that a proper setup for the HD800 to create a first-class listening experience requires components in your audio stack where the HD800 is the least expensive component!  

@Takeanidea In my back-to-back listening, the IE800 indeed proved to be very good.  To me, the AKGs have more detail retrieval, tonal accuracy, and a wider soundstage, but the IE800 was pretty close.  Perhaps the IE800 has a deeper soundstage vs. the K3003i with a wider soundstage, accompanied with the higher bass output of the IE800 and its more mid-range forward presentation.  The IE800, to me, sounds quite nice with vocals (albeit more coloured sounding) and the overall sound signature is smoother compared to the K3003i in my opinnion, with a tube-like sound.  It's interesting because I actually find the K3003i more refined, but the IE800 more energetic because of this.  For me, the accuracy of the K3003i's presentation and its wider soundstage makes it more preferable to the IE800, but both are top tier IEMs from respected companies and the technical differences between these IEMs are probably smaller than our personal preference of how the music should be presented.  I recall someone in the forums owning the SE846, IE800, and K3003i because they are different enough to have altogether. 

And in the end of the day:
JVC FX850 < ie800
ie800< AKG 3003i
AKG 3003i < Sony XBA-Z5
Sony XBA-Z5 < ak t8ie (mkI\mkII) 

I prefer the IE800 if I had to have one IEM in that price range. I loved the K3003i when I've heard it. But immediately I put the IE800s on I'm reminded why they are so great to listen to music on.
I managed to get a pair of cloned 3003s which come close to their sound. I agree with you on that they are totally different, it's probably unfair to say one is better than the other. They are both truly great earphones. Thanks for the insights. @RuFrost your reply makes no sense to me whatsoever. It looks like an equation and needs explaining 

Nice review.
Personally I'd never buy an earphone that has a permanently attached cable, regardless of their sound. I have the same opinion on the Shure KSE1500, and the AKGs have a much flimsier one, so not optimistic about this one.

Interesting review and comparisons. I love my K3003s very, very much. It's interesting to me that you didn't mention the (IMO) harsh highs of the K3003s. The first thought that crossed my mind when i first heard them was ''oookay this will be hard to get used to''. I have more than gotten used to it, in fact i absolutely LOVE the sound that it gives them. I still can't listen for very long without fatigue though.

Very nice review, but to clarify "....features a hybrid driver system with one dynamic driver and one balanced armature (BA) driver per side"

This is incorrect, each side has one dynamic and two BAs (triple hybrid). I truly love these and for 3 years they have been my go to IEMs. I recently came across the LZ-A4, same triple hybrid setup for under $200, bigger soundstage and simply stunning bass quality and detail retrieval. You owe it to yourself to try them. My k3003 have not left their leather pouch in quite a while (although I do still love them).

@Turrican2 You are correct.  I reviewed the manual again tonight and was reminded of the 3-way design.  Maybe I will give the LZ-A4 a try too.  The last time I ventured away from the K3003i and tried a Fidue A83, I was massively dissappointed and sold them pretty quickly. How would you compare the sound signatures of the two IEMs?

@Asiafood I did notice the extended treble at the very beginning too, but I don't mind them as it is very much crystal clear.  The treble was more fatiguing when I was using a DX90 as a DAP for the K3003i.  It was a great DAP with excellent clarity, but the sound signature was a bit anemic and treble happy.  At the moment I am enjoying music through a Headstage Arrow 5TX, which is highly customizeable (bass, treble, gain, and DAC ON/Off settings) and has a slightly warm sound.  

@audioscope not tried the fidue a83 sorry,

@Audioscope The treble is amazing in every way, no doubt about it. I use a Fiio X3 2nd Gen and a Fiio E11K. I have never heard anything else (except iphone 6 and HTC 10), but i've read that the X3 is a little on the warmer side. I think the K3003 performs incredibly well from those phones, the only improvement i notice with the Fiio DAP and amp is a little more full and dynamic sound.

@Turrican2 I think the Fidue A83 was not very good at all compared to the AKG.  There was no refintement and the soundstage was just not there.  What about the LZ-A4 vs. the AKG?  How do those compare to you?  

@Asiafood Haven't heard the X3, but I enjoyed the X5 as a reasonably priced DAP.  I suspect that the Fiio house sound is consistent in all their DAPs.  iPhone 6 played nice too - very smooth and a good pairing with the AKG.  I found that the AKG isn't terrible sounding even without the perfect file bitrates or a very expensiveDAP, and fairly forgiving, unlike some headphones out there.