Output / Input Voltage Question

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.

 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. 

The OP is complaining about too much volume with a low setting on the volume control. That’s why I suggested an attenuator like the SYS!
But as usual the self proclaimed Guru of high end audio likes to show his wit with a ridiculous answer to the problem that the OP is having!

@donvito I'm not complaining about too much volume.  Just trying to learn the reasons why.  I've always had a hard time understanding all things electrical. And the Sys is backordered until May!

If the loud volume on a low setting does not bother you then don’t fret. It would bother me. BTW, I use the SYS to tame down the volume on my CDP to match the volume on my turntable!!