I own Eidolons, but I can't comment on the Diamonds. What I will add, though, is an echo of Linkster's comments about associated electronics. I've heard Eidolons with Spectral, Rowland and Atma-Sphere amplifiers. I bought them based on hearing them with Rowland amplifiers. I love them in my listening room partnered with Atma-Sphere MA-2 tube amps.
For speaker cables with the Eidolons, I've used Goertz AG-3 cables and I currently use Omega Mikro Planar IV cables. The speakers definitely do not *require* MIT cabling, and the MIT would not be my personal first choice for this speaker.
The point here is that the Eidolons can be matched to a range of electronics and cabling - not just Spectral/MIT. As pointed out by Sbank, these speakers are extremely revealing -- you will hear everything in your system ahead of the speakers, for good or bad. But, they are not of the ruthlessly analytical ilk with unnaturally emphasized hyper-detail. With the excellent source material and associated equipment, the Eidolons will reward you with some of the most musically natural, nuanced and detailed sound reproduction you may wish to hear. And, the speakers will continue to further reward you for every improvement you make in tweaking or upgrading your system.
As to room requirements, the Eidolons will greatly benefit from being placed well away from front and side walls. That being said, I lived with them reasonably well in an 13'x17' room (placed 6' from the front wall and 3 1/2' from the side walls), but they sound even better in my new 18'x27' room.