Oh... I am very sorry I did not provide enough information. :/
I am using 2 rpi-2s. One with hifiberry DAC+ and other with hifiberry AMP+.
I used latest image for rpi2 and edited (SSH, VI commnad through Putty) the I2S as instructed.
But... When using Hardware volume control, the knob is stuck on 100%.
Software control is working as it should.