Matching a head/amp with the MM521s on my boat

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Hello. I am looking to replace my old Jensen marine stereo on my boat with a new unit, either internally or externally amp’d. I have four MM521s that I want to keep. Since each speaker is rated RMS 90w at 2.7 ohms, what should the optimal setup be in the amp in terms of channels, watts, and ohms. Thanks for your guidance.