It's highly advantageous to play around with both controls in order to match amp and pre. I would consider myself lucky to have such ability. You want enough gain in each to optimize sound quality and not too much as to cause distortion. And you want pre to have enough in relationship to amp's sensitivity but not so much as to overdrive the amp causing undue distortion. Hopefully other members will give a more technical explanation, but optimum settings will be dependent on speakers (and source). Will be dependent on how demanding are the speakers.
Volume control vs. attenuation control
Can someone please explain the difference between a volume control on an amp and an attenuation control on a pre amp. My pre amp manual states to leave the attenuation control at 0db for critical listening. Some amps have volume controls built in. So if I wanted more "play area" in the pre amp volume control (when playing CD's so the music isn't blasting at the 9:00 position) would it be better to lower the amps volume control or the pre amps attenuation control?