There are more changes required than what he points out... Also, the schematic he is using for the IIC+ isn't official. It's a fan drawn one by jrb32. They are indeed quite close, though. And as far as why you'd choose the amp over the preamp + poweramp, well... That is the age old question ever since the dawn of 80s rack preamp days, is it not? There are differences when the power supplies are decoupled like that.