Improved, high-capacity processing systems including a processing device such as an extruder (26) or a pellet mill (P) are provided which minimize product losses and permit the user to conduct multiple, segregated short runs with a minimum of down time between runs. The extruder systems (20, 220) include an extruder assembly (21, 221) having a special, multiple-position die assembly (28), as well as an upstream preconditioner (24) and feed bin assembly (22). A variable speed, variable output discharge screw feeder (78) is located between the preconditioner outlet (62) and extruder barrel inlet (90). A PLC-type controller (30) coupled to the extruder assembly components establishes a choke full condition at the discharge feeder (78) so that continuous uninterrupted flow of preconditioned material to the extruder (26) at a uniform mass flow rate is maintained for as long as possible. In preferred forms, load cells (46, 72) are operatively coupled to the bin assembly (22) and preconditioner (24) so as to monitor material flow through the systems (20, 220). A multiple stage cascade-type dryer assembly (29) is provided downstream of extruder (26). The assembly (29) is controlled via the controller (30) in coordination with the extruder assemblies (21, 221) so as to maintain the segregation between separate product runs throughout the drying operation. Pellet mill systems include bin and preconditioner assemblies (22, 24) operatively coupled with a pellet mill (P).