Using a power amp in your system is a whole new ball o' wax. You have to take into account the input impedance of the power amp and the output impedance of the pre-amp. Typically the output impedance of the pre should be far lower than the impedance of the power amp. This usually directs you to a proper rack mount pre-amp and not a pedal.
I use a 2KW capable stereo power amp but I designed and built a tube pre-amp specially to drive it bearing in mind the factors mentioned above. Good luck!