Well, I've gone with "uncovered" after having A/B'ed my covered/uncovered BKP's at volume the other week. I don't know why, but the uncovered Black Dog's in my Tokai just seem to have that nice aggresive edge that the covered Emerald's don't, even though the Emerald's have a higher output impedance.
Saying that, the Emerald's did sound fantastic.
Maybe with the next set of BKP's, I'll try some uncovered Nailbomb's... ;)