"I am about ready to break down and buy a pair of 208's and build Martin's (super simple ) BR design as so many other people have made them and been quite happy with them."

You will have the exact same problem with the 208 as you have now with the FE-206E. In my opinion they both require a filter to work well in a BR (or ML TL) enclosure. Before buying the 208's, why not try my Lowther ML TL with the FE-206E. You will need to increase the length of the port to six inches and add a correction circuit. The circuit that people are using is the same Zobel as my Lowther design with a 3 mH inductor in parallel with a 6-10 ohm resistor as a BSC circuit. The value of the resistor needs to be adjusted to mesh with the damping factor of your amp (lower for a tube, 10 ohm for a SS), your room, and your personal taste in bass response. Play with the value until things sound right. I have heard very positive feedback on this combination.

Martin