then the signal is not getting through the input bus on the MR8. Eitehr not getting out of the mixer or not strong enough through the unbalanced inputs on the MR8 (but you don;t need much of a signal to get at least get SOMETHING through the MR8 to make the bars move to show the input).
if you can hear the mix with headphone through the mixer and don;t have to crank the headphone volume then something wierd is happening. Try to plug instruments or whatever straight into the inputs of the MR8, if they show the moving bars and you can hear them, then you at least know that the MOR8 is functioning normally.
Oh wait, you don't have the MR8 in mastering mode do you?
Assuming that isn't the case, most mixers ahve several out options, main out, control room etc, switch through these and see if that works. Do you ahve any switchtes that route to control room vs main? Try to switch them out.
I have the same kind of setup working with a berrie mixer and it works pretty well. Whatever it is is probably jsut a button set wrong or something.
Daav