Preamp question about loudness

I am using a CDP with volume control directly into a 2WPC SET amplifier. If I add a line stage preamplifier, will the loudness increase? From the pre-amp specifications, is there any way to predict by how much the loudness will (or will not) increase? Thanks.
Depends on the speakers. Best way is to get a dealer to loan you a unit and try it.
If the preamp's gain is >1, the volume will be greater. However, the limit is already set(!) by your 2wpc amp. It can output only so much no matter how hard you drive it.

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.