So you're using the preouts of a receiver to drive an external amp, which then drives your Paradigms. And you want to know if you can simultaneously use the L/R speaker level outputs (i.e., the amplified outputs) of that same receiver to drive a different pair of speakers?
There should be no problem in doing that from the receiver point of view (unless, I suppose, you were driving a terribly difficult load).
Now, if you're going to drive two pairs of speakers (four speakers total) at the same time in the same room, many are of the opinion that you will lose imaging since each pair of speakers is rather designed to run on its own.
So, while the particular application may or may not be suboptimal for one's given preference, I don't think there should be any trouble with using your receiver in that way.
Good luck!