Pros: Good comfort, strong isolation, holographic instrument separation and uncanny imaging
Cons: Very dark, thick sound, hard to wear cable up, needs low impedance source
Along with the summary below, I have a review thread comparing the Sony EX1000, 7550, XBA-4 and XBA-40 here:
I also posted a Youtube review video of the XBA-40. If you like the video please check out my channel for more reviews :)
The XBA-40 has quite a comfortable design. Despite the large size of the earpieces they fit in my ear well and the light weight makes them quite comfortable. However, depending on the shape of your ear the large body may be uncomfortable with your outer ears. The revised elliptical cable with the new texture tangles less easily than the XBA-4 cable. The XBA-40 is designed to be worn cable down and doesn't work with cable up wear, which means microphonics is an issue (though not severe).
The XBA-4 is a very dark sounding earphone, and to some it might even sound congested. (Think Earsonics SM3). The bass reaches very deep and the mids have a glossy clarity about them. The one big improvement is that the metallic shimmer present in the XBA-4 has been corrected with the XBA-40. Bass also seems to dig a little deeper and more viscerally. Because of these changes, the XBA-40 seems even darker than the XBA-4! Because of the severe impedance swings of the XBA-40, the IEM is highly source sensitive and will sound shriller with sources with a higher output impedance. The real drawcard is that the XBA-40 has, lurking underneath the thick and intimate sound, a absolutely astounding ability to separate instruments and place them within a soundstage. I can think of no other earphone or headphone I enjoy more with electronica.
I would recommend the new revision XBA-40 over the XBA-4, but only for those who are fans of dark signatures to begin with. The XBA-40 is definitely an acquired taste and not nearly as balanced as some other earphones on the market. I personally really liked the XBA-40 and I especially love the improvements they made over the XBA-4 - but I would definitely acknowledge that it is not a good choice for most people, considering that even at a discount price there are more balanced dynamic drivers that are more balanced and more ergonomic (RE-400, GR07). Still, if you listen to a lot of electronica and you have a chance to get these at the current Amazon Japan pricing they are well worth it.