The deal on your amp is that the input is such a high impedance it's not a good match for the output of another power amp. It might be kind of noisy. But it will work just fine so just make sure you have a voltage divider network to drop the input down to 0.775v maximum.

Headphones outputs are usually voltage limited, but they are still relatively low impedance outputs.

Can you split the output from your disc player and run it to both amplifier inputs? That seems like it would be best. What prevents you from doing this?