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Recommend an Amplifier Wattage for this Sub Combo? - directed subwoofers

I carry two Kenwood KFC-W3009 12 "subwoofer in a box.
4 Ohms
Power range: 35-400 watts RMS (800 watts peak)
Frequency response: 25-800 Hz
Sensitivity: 93 dB

I also use the D600 with the director of audio amplifiers,
Type of Class D Mono
-Maximum power 600 watts
RMS Continuous Power - 300
Freq. Answer-25-250 Hz

I think I need an amp is too small?
What size would you recommend?