Yes it can be that they were used as normal single digital inputs which means they need to be configured for MD1 and MD2.
It can also be that the wrong output is connected to the input on the 861, with that I mean for example the centre and sub channel to the connection of the fronts.

861v4/ID40, G98, UHD722, Mark and Levinson No. 29, 2 * Linn LK85, Linn LP12, Musical Fidelity X-LPS v3, Empire Vandenhul MC1000, NVidia shield, PS4, Thiel CS2.4, Thiel 1.6 rear, Audio physic Celcius centre, Rel Quake Sub