Get the vendor use meter to test the RMS does it meet the value as specify on the amp. Many of China or local product doesn't meet. Also test out the duration of the performance. Some amp get overheat easily, and the quality will drop after some duration of continue operation.

Yes RMS come from calculation. It would be the most accurate way to measure power is RMS (root mean square) watts.

The RMS value is obtained by squaring the value of the signal, taking the average, then the square root. This is the equivalent of the actual power delivered. Most reputable manufacturers use the RMS rating.

To get RMS power from peak or max power just divide by three. Music power is just half of peak power. For example, an amplifier is rated at 100w (peak) per channel. The so called Music power would be only 50w per channel. The RMS power would be 33w per channel. Big difference, isn't it?

Just be careful when checking specifications of amps before buying, to see what you are really getting. Always ask for the RMS power of an amplifier.

I though every woofer have to get the spec then messurement on the box. Diff messurement for box come out diff frequency range. Am I right?

Ported / vented box more "high bass" on hearing compare to sealed box.

I refer to the link the amp spec is below,

Frequency Response 10Hz~40KHz
RMS power at 4 OHM Stereo 80W x 2CH
RMS power at 4 OHM Stereo 250W x 1CH
RMS power at 2 OHM Stereo 130W x 2CH
Max Power 400W
T.H.D 0.05%
Input Sensitivity 200mV~4V
Input Impedance 10K ohms
Damping Factor >200
S/N Ratio 100dB
Channel Separation 60dB

With base on the spec u given on speaker is RMS 300W, I would say not enough power to drive. The amp only give RMS power at 4 OHM Stereo 80W x 2CH.

Please do correct me if I'm wrong.

2ch amp bridge become 1ch = only driving 1 sub-woofer.
Yes the amp will produce (b), but only for 1 sub-woofer.
I conclude that the amp not suitable for your requirement.

CaLz, get comfirm the sub-woofer spec, then will be easier to match. 300w is RMS or peak?