Tony- Disc 1 and 2 are phono inputs. As such, they will provide a much higher level of gain than you should need, which may or may not be a problem in your particular set-up, but they also will overload easily with a line level signal (particularly when the head-amp is ON) and more importantly, will alter the tonality of the signal by passing it through the RIAA equalization circuit.
So they will work with a line level signal but will not preserve the proper tonality.
So they will work with a line level signal but will not preserve the proper tonality.