Is there any objectionable hiss when listening to your sources with out the eq installed? Has the hiss level with nothing connected changed lately? This is a vintage receiver that might need service (as is the eq).
Otherwise, a hiss problem might be caused by an impedance mismatch, although that should be unlikely with two components from the same manufacturer and of the same vintage. As an aid to diagnosing the problem, I suggest trying to patch the eq between the pre-out main-in loop on the receiver (receiver pre out to eq in, followed by eq out to main in on receiver).
While using this arrangement is generally not preferred when other options are available (such as the one referenced by STaL), the voltage going to the eq will vary depending on the volume setting of the receiver, which in turn may affect the level of hiss, or eliminate it.
Good luck and let us know how it goes.
