You will be "double terminating" the Coax output. But if it will handle driving 1/2 load, it might just work as long as the two receiving units don't interfere with each other (shouldn't). Otherwise a Coax SPDIF Distribution Amplifier/splitter would likely be needed as linked to above (that's NOT a switch box, but a 1x2 active distribution amp).
Alternatively, you could also convert from Toslink SPDIF to Coax for the 2nd feed (set the Toslink Optical to "SPDIF" on the FF400). I'm not sure if the FF400 allows discrete Optical/Coax SPDIF source signals (doubt it) - but that's not one of your requirements
MADIface-XT+ARC / 3x HDSP MADI / ADI648
2x SSL Alphalink MADI AX
2x Multiface / 2x Digiface /2x ADI8