You can't select on the amp how you want to run it. It's all based on the sub and how it's wired. IF the sub is single voice coil, then you're stuck running the amp at whatever the sub is. If the sub is dual voice coil, then you can wire it in series or parallel to have different impedance. From what I can find, it seems that your sub is a 4ohm sub. If I'm right, you're stuck running it at 4ohm.