You are wrong in more than one way. I was advised several times to buy an E12 to solve the lack of amp power on the X5, and nowhere on the Fiio website says that you lose such an important adjustment as the balance control when you add the E12 to the X5, a combination that Fiio DO recommend to buy. Let me repeat it for you: Fiio recommends to buy the X5+E12 combo. Who's to blame if that results in missing functionalities? The customer who can not know that in advance because the company that sells the product do not care to inform it?
Any company should warn what functionality will be lost or what important changes will occur when something they sell is added to another product of their brand, specially when they are sold together as a bundle. This is called common sense, or best practices, if you prefer.
And no, I'm not kidding, I am reasoning.