Is it safe

Not a good idea. Thee output of one of the items connected will 'see' the output from the other as a voltage coming in..
Most audio product outputs do not do so well with a strange voltage entering the output transistor.

So in general no it is a bad idea to connect to outputs to the same input (Even though one is turned off) for the above reason: the voltage is presented to the output stage of the turned off item.. and that is usually bad.

No, not a good idea at all. Use one or the other, not both.

Also it says to NOT DO THAT in the 502P owner's manual on page 8, section 1. Distortion will occur. Really...that's what it says.

I talked to the tech at Jolida and they said it should not be a problem as long as only one source is operating at a time.However if I understand what Elizabeth is saying the problem is not so much in the amp as it is with the other source receiving a voltage on it's input.I assume that there is nothing in the circuit to prevent a back flow of current through the other source.Wolf_garcia the manual says "Only one input signal should be operating at one time,If both inputs are RECEIVING an input signal, the result will be distorted sound." the way it is worded makes it seem that it would be okay as long as I was only sending one signal at a time.I guess for right now until I know for sure I am not going to blow anything up it will be one source or time to get a preamp that handles more than one source.