CC2543 ADC differential input

Hi,

Please tell me about ADC differential input(CC2543).

*Question
I want to input Audio signal using a function of differential input.
By the setting of this register and the connection method of the plug, will Differential-input function?
I feel that differential-input does not function even if I perform this setting in my environment.

Please tell me the mistake ている point.

*development environment:
    SmartRF05 Evaluation Board　Rev.1.8.1
    CC2543
    Mic Input Balanced(Hot,Cold,GND)

*Setting of ADC Registers:
    ADCCON2
        SREF  11: External reference on AIN6-AIN7 differential input
        SDIV  10: 256 decimation rate (10 bits ENOB setting)
        SCH   1011: AIN6-AIN7

*Plug connection:

    Audio signal            CC2543
    Hot Plug 　　　--> 　　AIN6
    Cold Plug 　　 -->     AIN7
    GND Plug       -->    GND