I heard the Diamond series a short while back---they were priced at around 8K (?), don't remember the exact model.
They were being fed by a 4BSST-2, BP26, and BCD-1. Had I not known they were Diamonds, I could easily have heard them as a previous B&W series, or even some other "XYZ Wonder Speaker--Sapphire".
So, they sounded very nice, but not so nice that I'd rush (or even mosey) out to spend the extra dough on them.
I actually considered going for a previous/earlier B&W offering (800 non-diamond series) at almost half the price.
The diamonds are good, though, no doubt about it.