That's not a bad amp. It is RF's older amp. I'd personally get an amp that was higher powered than the sub. The idea is to maximize the sub before reaching distortion level on your HU (around 85%). Therefore, if you had 400w amp, at 75%, you would be gettting max power for your sub.
Of course what glasswolf said is true, but you have to remember, almost ALL HU will distort near maximum volume level. So I'm just recommending that you get the most power out before reaching that point. If your HU is 4v out, then set the gain to 4v. In theory, when the volume is set to max, it should send out 4v to the amp. That will cause the amp to produce rated power. Now if you had 400w rms amp, and set the volume to 75%, you'd be getting almost 300w of clean power. Speakers do not blow from getting extra clean power. It is distortion/clipping that causes breakdown.
ok so i have a panasonic C7000 series HU with the full dot matrix display. so your saying that if i set the gain to 4v than the amp would not send out all of its rms, or am i not understanding? when you say set the volume up to 75% do you mean the actual volume b/c i thought the amp always sent out its peak rms no matter the volume.