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.

Wilson667, the guys here are full os s$$$ re. answering your question - it should be OK for you to connect both sources to the Jolida jd502p PROVIDED ONLY ONE SOURCE IS SWITCHED ON AT ANY TIME & THE OTHER SOURCE IS SWITCHED OFF i.e. OFF OFF/COMPLETELY OFF.
The output stage of any component is designed to handle source/sink or push/pull current of fairly large amplitude and the output voltage spec is usually 2V for many line-stage components. So, for an SWITCHED OFF component to see upto 2V on its output stage should be no issue at all - it would be a voltage within spec. Also, there is NO back flow of current into the switched off component because it's off! Current flows only when the 2nd source is powered on & the transistors inside are biased on. When the 2nd source is powered off, the transistors are biased off i.e. they do not draw any current except for some leakage current in the mirco-amps region.
All of this assumes that you will be very diligent in ensuring that only one source is switched/powered on at any one time.