You can of course split to 3 consoles and have separate channel processing on each position but then it´s only possible to use around 42 ch at each position. Or eg. 50/40/38 or what you choose yourself. Of course everything else needs to splitt as well (FX, Auxes, DCA, Groups etc).
Otherwise a DM0 as Steffen says with a G-ACE card in each mix rack. But then it´s not possible with gain-compensation to the DM0 system.
/Peter