Just the facts....don't kill the messager, but an 8" driver is going to be beaming at 5khz (due to size of wavelengths) and making crossing to a tweeter *very* difficult and unnatural sounding. A 3-4" driver is pretty much required if beaming is to be avoided up this high. Then the low end requirement becomes crippling at higher spls. 4" drivers don't move much air. That said, take a look at the Three way driver study thread on HT Guide.com. Really good research being done there on mids for similar requirements.
So far, a 4" tangband is in the running for modest budgets and the Accuton C79 & C89 are in the running for more healthy budgets. These are 3-4" drivers. They are probably not going to be used quite as low as you mention, at least not nominally, but they will be crossed 2nd order so a lot of info is still coming from them.
Dueland's xo requirements make for an interesting design. If it works as is theorized it could mean the xo is truely not audible, since all off axis sound is in phase at *all* frequencies, not just on axis response.
