The only thing a preamp will do is increase the output voltage of your CDP by a some factor given by the gain (usually in dB). However whether this increases loudness compared to your current solution depends on the maximum voltage output of your CD and the input sensitivity of the amp.
How far is the volume turned up on your CDP for loudest listening? Can you turn it all the way up? Most likely the loudness is limited by your amp's power output and speaker sensitivity not by your CDP or preamp gain.
How far is the volume turned up on your CDP for loudest listening? Can you turn it all the way up? Most likely the loudness is limited by your amp's power output and speaker sensitivity not by your CDP or preamp gain.