http://www.harman-japan.co.jp/product/jblhome/4429.html
The site mentions that it is the descendant of the 4425/4428 with "new" technology down trickled from the K2 S5800 and DD66000.
Retails for approx USD 5,200/pair
Below is the 4428 for comparison
http://www.harman-japan.co.jp/product/jblhome/4428.html