My Sony MDR 7550's arrived!
Before I got the EX1000, I looked at the frequency response graphs comparing the EX1000 to the 7550 (both Sonove and Tyll have them graphed) and tried applying an equaliser to the EX1000 to guess how they might sound. (-2db at 2k, -3db at 4k, -5db at 8k, -3db at 16k in iTunes).
Welp, the 7550's really do sound pretty much like that. A smoother sounding EX1000 which takes the edge of some of the more grating sibilance peaks of the EX1000 but also loses some of the airy spaciousness and ambience of the sound. This does rob the EX1000 of their character somewhat, but does make the IEM more friendly for more genres and preserves their actual ability compared to their perceived detail.
The differences in build are a mixed bag. I love the longer (1.8m) cable for desktop listening, but its obvious that the materials used on the 7550 are of a lesser quality; ie: the cable is less supple, there are rubber seam joints on the ear guides, the (metal?) shells look like cheap black gloss plastic and not that dark burgundy of the EX1000's magnesium housing. They still have great build quality, it just doesn't scream premium like the EX1000. However, the overall lighter weight of the earpieces takes the EX1000 design which is already comfortable, and makes it even moreso.
It doesn't seem that these changes make a great deal of difference to the actual sound though, given that the EX1000 and EX 7550 graph almost identically. Apart from the filter design and port size, I would guess the difference in measured distortion comes down to the EX1000's LCP driver.
Might be a bit early to draw conclusions, but the 7550 seems like a good value alternative to get the EX1000 sound without the peaks. (Kind of like how the CK90Pro relates to the CK10). And if you aren't adverse to EQ, the EX1000 can be turned into a premium 7550 preview in a jiffy.