I agree with everything Duke said. It's been a while since I've listened to the Fostex Fe167. I forget what model of Fostex's it was, but it was one of the smaller FE series seemed like it started going cone breakup mode, or rolling of between 6k-8k, but people were x-over betweem 8k-10k with just a cap to add the extra high-end extension. Jim Denton or Akhilesh should chime in, they've used Fostex's in the past.
Bill W.P.S. The Fostex FE206E is one of the smoothest single drivers I've heard.