Aren't those components designed for each other? If you're still hearing something wrong and the preamp has been serviced, I'd get the amp checked out if you haven't. A general rule of thumb is to make sure the output volts of the pre is at least twice (preferably more than that) than the input sensitivity of the amp. If you have that you should be fine.
Power Amp Pairing
I have a Pioneer SPEC 4 amp and SPEC 1 pre-amp. The power blew on the SPEC 4 in January and the repair is complete. There is, however, still some slight distortion coming through the right channel (I've checked everything...different speakers, different speaker wire, etc.). With the length of time it took to get it repaired, I'd prefer not to take it back for further repair. So, the question is: can i purchase a new/used power amp of ANY brand that will pair nicely with the SPEC 4? If so, what i do i need to consider or be careful about?