When using the Lutron spacer system with the Accessory dimmers, you can forgert about the 3 way and 4 way stuff. You really have the main dimmer with Accessory dimmers to control it. The main dimmer is typically in the box with the power feed (line in) and the last accessory dimmer box usually has the lamp (load) wire coming into it. IF this is not the case, you will use the spare wires from the old three way/ 4 way setup to complete the electrical circuit according to the spacer wiring diagram. I am assuming you have one.
Do you have some way to link us to a diagram you have made of the electrical layout in your basement?