2 Pre amps: Huge volume difference??

I am testing two pre amps (different models) of the same manufacturer. On one of the pre amps, the more expensive one, I have to increase the volume significantly to get the same volume as the other pre amp. What the heck is going on? My amp seems to be working harder.
Output "impendance" of PRE is mismatch with Input "inpendance" of the amp. Bigger the difference, between the two "imendancie's", better match! Idealy ratio 100:1 (10kohm-100ohm) Good Luck!
Perhaps one is a passive model and the other is active--and even if they are both active there could be differences in the amount of gain each delivers. There could also be differences in the tapering of the volume controls. Anyway, the arbitrary positions of the volume indicators on preamps can vary quite a bit from model to model. As long as you get enough volume from the system, does it really matter if the knob points to 9 O'clock or 2 O'clock? Also, many have suggested that volume controls are more linear in their performance characteristics closer to their maximum settings. This has nothing to do with making the amp "work harder". It has to do with supplying the same given voltage at a different point on the dial or indicator. Since the preamps are from the same manufacturer, why not give them a call--they ought to know!