As per the specs, it likely has a lot less than 200 watts of real power in total. When they claim "Full Bandwidth Power (at less than 1%THD) 22W X 4" then it's probably even less than 20 watts per channel when checked at under 1/10% distortion like good home audio equipment.
It's a budget device, touting a lot of features like changing colour displays, bluetooth, USB charging, Alexa etc. and how many phones can connect before it even gets to the sonic abilities. No doubt it sounds better than the original 2 or 5 watt radio though.
Because of that i would say if you really want to use the internal amplifier you want speakers with no more than 22w RMS @ 4 ohm each.
But its still taking a guess to some extent.