At the request of Kunlun, I spent a few hours listening to the Z5 this afternoon along with the Sennheiser IE800 and a few other Sony models - EX1000, H3 and 7550. After that, I broke out the Roxanne UF and FitEar 334 just for fun. It was quite enlightening.
Some things I learned:
1. Sony can make really good dynamic drivers
2. The Sony models are more alike than they are different and I really like all of them.
3. I really don't care for the IE800.
4. There is a good reason that some IEMs are priced at over $1000.
I listened to a variety of 16/44 and 24/96 tracks, mostly acoustic, from an AK100/Vorzuge Pure II combo.
I had forgotten how good the EX1000 is. Excellent bass, good detail, very natural sounding strings and vocals. Since I'm over 50, I have enough high-frequency loss (mild) to render the EX1000 treble quite bearable.
The H3 adds a bit more bass and has even more detail. The H3 is quite a bit bigger physically and makes the EX1000 look positively svelte. The bass decays a bit slower that the EX1000.
The Z5 adds a little more of everything - more detail, more and deeper bass, but the bass decays even more slowly than the H3. I only have about 75 hours on the Z5, so it might still tighten up a bit. It's not sloppy, just BIG.
The 7550 is very similar to the EX1000, but smoother, especially in the treble. This is the one for long listening sessions.
You can really tell that the Sony models are all of the same family when you compare them with something else. The IE800 sounds like it is from a different planet.
The IE800 bass is almost over-controlled compared to the Sonys. Very fast decay. The midrange doesn't sound as natural to me, especially vocals, which sound a bit thin. The IE800 sounded much less spacious and airy than the Sony models. Almost like listening in a dead room. It even manages to have worse ergonomics than the Sonys and that's saying a lot.
So, just to bring some perspective, I dug out the Roxanne UF and FitEar 334. Both of them are in a different league than the Sonys and IE800. Deep controlled bass, great detail, while still having a very natural tonality.
For the music that I listened to today, I preferred the 334 to the Roxanne. The Sonys were all very good, just not in the same league. The IE800 is going up for sale.