need help with adding active mixer?

Hello .i need help with adding a active mixer before the "MXR headphone amp" .

The images bellow are the original schematic and my new schematic

my question is :
1.will this circuit work properly ?
2.i need the gain of mixer = 1 , so Ra=Rb=Rc=Rd , but what value should i use ?
3.What value should i use for Ca,Cb,Cc ?
4.What value should i use for Rx

Thanks in advance!
sorry for my bad English!

Picture of need help with adding active mixer?
I'd say try 10K for the resistors and 0.47uF for the caps - but use something like polyesters. Basically, you want the impedance of the caps to be << input impedance of the amp, which is set by the resistors you use. The impedance of the caps is 1/2 pi x f x C - guess at the lowest frequency you're expecting a response at.

Rx should ~4.7K (Ra // Rd) , but I hate that biasing network - you WILL insist on using it, despite the fact its output impedance is very high. You really should use a unity gain buffer instead.