Personally I find that the Fostex bicones change over the long haul as well, sounding better over time, with 200 hours being a bare minimum mileage before you can even hear what they are all about. The Sigmas take even longer, the 168 about a year of almost constant play. And a good workout. Curiously, the FE166esr sounds great, after 10 minutes you forget all about break in.
It is my belief that some never actually hear how good those speakers CAN sound, because they never get loosened up enough, or are allowed enough time on them. The spiders are Stiff As Hell. Patience is the word.