How far away would you be sitting from the soundbar?
Assuming the 93 dB efficiency rating is true, then you would be using about 1/4 watt for an 87 dB sound level (at one meter, it gets lower as distance increases). That is quite loud. Going from a 50 wpc Marantz to a 100 wpc Marantz/Denon/whatever buys you only 3 dB additional headroom. Depending on your listening habits, and seating distance, this may or may not make a difference.
You might want to download a dB meter to your phone and see what sound pressure levels you will be most comfortable listening. This will tell you a lot about your speaker efficiency and receiver power needs.
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