Your amplifier is NOT STEREO STABLE AT 1ohm.
Stereo requires a L and R channel. That means two channels. You have a mono/single channel amp. It is stable at 1ohm but because your power supply is regulated it doesn't put out any extra power. Therefore, wire for 2ohm because there is a slight advantage and it NEVER makes sense to wire for lower impedance unless you gain power for a specific application/purpose that usually isn't music related.
If you were pulling more than 20amps then it would blow the fuse. How long is the 8awg?
Wait...you wanted more punch too? Most people don't know this but your midrange defines the characteristics or sound of the subwoofer(bass). Being out of phase can kill the midrange and sub too. Try swapping phase by reversing + and - wires on the sub or amp...amp is probably easier.
