As has been stated, if you have no issues with control over your volume, you are happy with your sonics, them you need not be concerned.
Many amplifiers require over 1V to reach full output. Your amp requires only 0.5V, making it more sensitive to input voltage. Therefore you are attenuating much of the gain provided by the preamp, via the volume control.
Many amplifiers require over 1V to reach full output. Your amp requires only 0.5V, making it more sensitive to input voltage. Therefore you are attenuating much of the gain provided by the preamp, via the volume control.