Just to comment about the phase concern. It appears the two drivers are inverted phase mechanically (that is one driver is cone facing out of box while the other is cone facng into the box) and then electrically inverted with reference to each other. End result is that both drivers are then in phase in reference to the box. There would be almost no output due to cancellation if the drivers are actually out of phase. The reason the designer would do this is to eliminate non linearities of the driver. No driver has a constant magnetic field as the voice coil moves through its travel but by having two inverted drivers as this does any non linearities are at least now summed to be symetrcal in either direction of travel from neutral. And it looks rather cool too.
I do not think it is wise to weigh in a discussion about the most suitable design for surrounds but I did notice this link when I went to check out the unicorns design. At this price I say buy a couple and give it a try.
Don't get me wrong. The Elektra is very highly regarded, and I truly believe it is a world class product. For hard to drive speakers, you can't go wrong. If you want to squeeze the last 10-20% out of a really good pair, and can afford it. Then why not.
Rather than thinking about it with a negative attitude towards the Elektra, it makes me realise what a quality product my Marantz is.
I also like the idea of adding a second sub into the system down the track. Unfortunately I then looked at the current version of my Velodyne 10" and they have doubled in price in the 5 years since I bought mine.