Tboooe, gain is gain no matter what the maximum output is so that would not be the issue. Input voltage times gain = output voltage.
However, the stated gain is with the volume control all the way up. The taper of the volume control is usually not linear and may be different for the 2 preamps. For instance, one preamp with the volume control halfway up could be near full volume and the other one only at half volume.
Tony, an attenuator can indeed by made with a single resistor in series with the input. As you conjectured the input impedance of the amp is the other resistor in the divider.
Although I would prefer not using one if I dont have to, Im not as dead set against using an attenuator as some. After all, the volume control is simply an adjustable attenuator. In most cases I would use one at the input of the preamp though instead of the input to the amp. The signal from CD into pre is much hotter than from pre into amp, the input impedance of the pre is usually much higher than the input impedance of the amp, and Pass amps are among the lowest. If you find a pre you really like any competent tech should be able to pad the gain either at the input or at the volume control.