if you read the specs from that amplifier...
20w at what ohm resistance? its not 20w across the board. they are rated 4-16ohm and it could very well be it is 20w at 16ohm (or 8ohm, no way of really knowing without looking in depth)
if you read the specs from your speakers
Recommended power: 20–100W
20w@6ohm is the lowest that they suggest to power the speakers however you will want something quite a bit more than that if you want to really get your money out of them. at minimum i would say 50w@6ohm however preferably 80w-100w.
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TLDR: yes, too good to be true.