I doubt if there is any danger but the impedance effects are indeterminate. Try it or, as I would prefer, convert one of your sources to TOSlink or other. (Or add a P1A.)
The P3 will accept "coaxial S/PDIF, optical TosLink, AES/EBU, and I2S 5-pin mini-DIN connectors."
The P3 will accept "coaxial S/PDIF, optical TosLink, AES/EBU, and I2S 5-pin mini-DIN connectors."