Hi sorry i did get back to earlier and thanks for the pictures.I like the OB very much but i am wondering how big they are and how do they perform,specially when it comes to low freq.Regarding the difference of performance of your 604 E vs C,they are indeed different drivers with different surround and i doubt that the the GPA crossover is equally adapted to both of them.There is also a distinct possibility that your E and your C are not in the same"shape".Did you check the surrounds,the spiders and the level of magnetisation of both pairs?
Charles;