Hi Norbert,

I used the PIC16F1825 in a recent project with ADC input on AN0.
I used FRVCON = %11010011 to enable the fixed voltage reference and set the voltage to 4.096V.
Your ADCON0 = %000110001 is correct for selecting AN6 as the ADC channel (RC2).
To apply the fixed voltage reference to the ADC you must set bit 1-0 of ADCON1 to "11"
In my application I used ADCON1 = %10100011 to right justify the output, set A/D clock to Fosc/32 and set Vref- to VSS.
You may need to change the A/D clock selection depending on you own oscillator choice.

Cheers
Barry
VK2XBP