Your amplifier has very high input impedance, so your series resistors can be high too. The higher resistance you go, the more isolation you'll have. That will improve stereo separation on the pass-through plug signals. I think I'd probably go with 22k ohm in most cases, but you might try 100k first and see how it works. Might even get away with something between 100k and 470k. What we're looking for is the highest value that doesn't attenuate the sound level.Connect one end of the resistor to the left RCA center and the other to the the circuit "in." Do the same for the right RCA center, both connected to the amplifier input It forms a sort of a "Y." Then you can connect a second pair of left and right RCA plug straight to the first pair for a pass-through connection. Don't put resistors between the RCA jacks, only from the RCA jacks to the amplifier input.