Bernie,
I used to use FE166E's in alot of enclosures.
Here's the direct replacement I'd recommend:
http://www.madisoundspeakerstore.com/approx-6-fullrange/fostex-fe166en-6.5-full-range/
I find it pretty hard to tell a difference in the sound of the 166En, and my guess is that in the sealed box design of the Sexy you can get by with prettymuch anything...
Hope that helps,
Cheers!
-Clark