It really depends on how the Marantz handles "bi-amping". If the Marantz will send the same signal on both bi-amp outputs, then you should be fine with experimentation. However, I have seen some receivers that handle bi-amp in a weird way. They will use an active "comparator" circuit to determine the frequencies that the "bass" bi-amp output is actually using. Then they will subtract those frequencies from the signal and output the "difference" on the high bi-amp output. The result here is significant loss of sound quality.
In either way, I don't think you'll be getting much benefit because both bi-amp outputs will share the same power supply in your Marantz. I have heard others that report an increase in sound quality. If your speaker wire is all run through walls, then it may not be worth the effort.