The 1.5V is for the amp to deliver it's FULL POWER. You don't want that to happen. So you have the volume control to control the entire 2.2V that the CDP is delivering to the preamp. The preamp will start with 0 and go up from there. I don't know the specifics of your amp, but if your speakers are not sensitive enough, I suggest the Balanced over RCA.
Yes, Balanced will have a slight hum if your speaker are sensitive and your ENTIRE setup is not Balanced.
Yes, Balanced will have a slight hum if your speaker are sensitive and your ENTIRE setup is not Balanced.