am i underpowering?

[cyberbob25 10+ year member]

Subwoofers are what create resistance (measured in Ohms). If you have a 4Ohm subwoofer, this means that it presents 4 Ohms worth of resistence to your amp. You can't just 'throw' ohms at a subwoofer.

 

[80_Cutlass_mn 10+ year member]

Subwoofers are not stable to anything. Amps are the only thing that are usually labled 4-2-1 ohm stable not subwoofers because subwoofers are what creates the 4-2-1 ohm resistance that the amplifier "sees". So what cyberbob25 said is true.