general

Friend

It can be done, but the impeadance, load, and other measurements will be inconsistent and will not sound too nice!
Step down transformers can help with these things, but the money spent on those could be spent toward some great amplification.

If I understand correctly, you want to run the output of a preamp into the inputs on a receiver. You might be able to do this two ways. If your receiver has "amp in" rca jacks, you can use just the amp portion of the receiver. If your receiver does not have "amp in" jacks, you can run the wires into the Aux (or tape) input. Keep the volume control on the pre-amp fairly low to avoid overdriving the inputs. Raise the level on the pre-amp to the point where switching to the radio on the reciever gives about the same loudness from both sources. It should not harm the preamp if you hook it up properly.