You know, I got the xba 40 paired with the e11. I do agree that the xba 40 is a bit dark, but after some experiments I find that it's a bright iem if you so choose it to be. In fact, I felt the treble was a bit off, kind of veiled. All I did was replace the silicone tips that came with the xba 40 with normal black sony silicone tips and suddenly the treble became uncapped, it went up a pitch or 2 and felt more natural sounding, and airy. The bass was only affected by actually becoming more detailed 0_o, still as deep and rumbly as ever. I liked it before but now I really love it with the tip mod. I feel it didn't actually shift the entire sound spectrum upwards, but actually expanded it.
The story is that I once got the sony mdrex58v for $20, and I loved the crispness and clarity, but it broke. After getting the xba 40, i bought the 58v again to compare, and it was more detailed than the xba 40 to my slight disappointment. I then proceeded for sheeps and giggles to switch tips and the result is what you see in the 1st paragraph. I don't know if the tips from the mdrex58v is exactly what is being sold by sony on amazon though.