What preamp do you have? 1.5V output from a preamp is very unusual. That's even lower than what most (if not all) digital source components provide which is around 2V for single ended outputs.
Output / Input Voltage Question
If I have a preamp that outputs 1.5v, but the amp's input is .5v, would this be the reason I don't have much headroom when I turn the volume up? What is an ideal voltage match for preamp/amp combo? Sorry if this is a dumb question. Electrical stuff is not a strong point for me.