Another dumb question

Slartibartfast has the right point. Very often high powered amps require higher input voltage and so you should match the preamp for your new amp.

No dumb questions ;just dumb answers. Sounds like a gain situation as descrbed above; good answers.

I think in many cases the input sensitivity of the amp needs to be almost 100 times that of the output sensitivity of the preamp for a good match. This varies however depending on the particular components and/or manufacturers being matched up. I've run into this same problem but only when trying to integrate a powered subwoofer. Good luck.

I'd buy a new system if I were you :^)

Sdcampbell is quite right. In general, the higher the position of the volume control knob, the less negative influence the attenuator will contribute to the sound. (The best potentiometer is no potentiometer.) However, there were/are a few old preamps still floating around out there that used the "pot" in the op-amp feedback-loop to actually increase or decrease the gain of the circuit, not as the typical in-line signal attenuator. Thankfully, not many attempted this as over time the circuit stability and sonic performance suffered. Gunbei- I think you're referring to amp input and pre-amp output impedance, not sensitivity. A ratio of 100:1 is an ideal. In practice, if cables are kept short, I've had good results down as low as 15:1.
Enjoy the music!