Hey Bob,
yes, that is true. Just like the Raspberry Pi in the Onefinity Controller is connected to the AVR board, and the AVR microcontroller to the TI stepper drivers, you would need motor drivers between the PC and the motors, there are suppliers for such parts. Usually you also add an I/O card in order to have enough I/O ports, to drive the motors and also other things like additional limit sensors. For each axis motor, you need one port for step, one for direction and one for enable, so you are already at 12 if you have 4 axes so even if you have an ancient parallel printer port, it would not be enough, hence the need for an additional I/O card, which is usually connected to the PC via PCI or PCI-E but also via Ethernet. The MESA cards are used by many for this.
You may wait for the Upgrade to Elite that is announced for the future 