2 ohm or 4 ohm

The subs are dual 4 ohm, so they will either be wired in series for 8 ohms or in parallel for 2 ohms.  They should be at 2 ohms.  Look at the left column under "woofer wiring" to see what the wiring should look like.  You would look at "one 4 ohm DVC sub" wiring because each sub has its own amp.  Pull a sub from containment and look at the wiring.  Although the subs are rated at 300 watts, the mono amp's output loaded at 2 ohms should be fine because it doesn't greatly exceed the sub's continuous power handling capacity.

If they are already wired at 2 ohms each, you should be enjoying 600 to 700 watts of subwoofer pounding.  If that's not loud enough, there are other issues you need to look into.