With dual 4ohm coils you have two options. Wiring the coils in parallel with give you a 2ohm load (both positives together and both negatives together) and wired in series will give you an 8ohm load (not very practical with a single sub). You can either run a mono amp that is 2ohm stable, a two channel wired 4ohm stereo, or a two channel bridged mono with a 2ohm load (check before buying that it will run at 2ohms bridged).