With the FE208E's low Qt (0.18) common wisdom would be to look for horn loading. Qt of 0.4 is more in line with bass reflex or transmission lines. Bob Brines (http://geocities.com/rbrines1/) sells plans for smaller Fostex drivers, but it's a transmission line based design that looks much like a bass reflex cabinet. Tom Zurowski (http://audio-resolution.com/zhorn/) of Z-horn fame sells a rear loaded horn cabinet for the FE208E called "Garuda".

Steve has his new High Definition Tower design that uses the FE208E, but that's perhaps the most complicated design I've ever seen (has lenses, port, two passive radiators, and a transmission line). Classic Audio (http://www.oldhifi.com/) sells bass reflex design for the FE208E in a variety of sizes and Steve built a rather small standmount bass reflex for it as well. We heard all of these at the 2003 DecFest:

Steve's HDT uses modified FE208E's (treated = ??). The prototype sounded pretty good, but the untreated driver was still breaking in.

The Classic Audio 2.5 sounded less flat, more boomy, and the side panels resonanted when struck, but received less play from the new drivers.

Steve's small standmount I thought sounded quite promising if used with a sub, but received little play from the new drivers.