I built some Fostex BR 206E's. I know these aren't the optimal enclosure, but they sound mighty fine. The Fostex line is great, though they don't excel at metal/rock. In fact, I'd say these are worst with this genre and significantly better with others.
These drivers are peaky from about 1 - 4 khz which is where the guitars live. It gets grating unless you have some (hopefully minimal) circuit correction. Even then, these drivers aren't made for that.
Check out the Zu Druids. I own them. 101 db at 8 ohms. They play everything. Loud, whisper, girl with guitar, Metallica, club/dance music. They kick booty at classical too. Plus, my 6 watt amp is a titan with them.
The XOverless thing is the wave of the future. No big amp/speaker combo I've heard can touch single-drivers in transient/vocals. With the Druids, the thunder aspect you'd expect with big amp/speakers is there too.
How they can bridge the gap so seamlessly astounds me every time I turn them on. It is a paradigm shift in the making and this is not the last time you'll hear this.
FWIW my last speaks were Gallo Ref. 3's and these utterly kick the tar out of them in every way. On 6 watts. Incredible.