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You can use both speaker sets, they would connect to the back of the amp output A and B.
The only benefit would be if you have a second room. I would not recommend to put the 4 speakers in the same room.
Some people like it I think it sounds kind of strange, but test it you may like it. If you do it pay attention to the polarity of the speaker cables.
If you settle for one pair use the concept 40’s, the sound better and they are rate up to 150W your Amp is rated 100W.
The Concept 20’s are rated 75W, so your amp has the capability to damage the speakers at high volume setting.
Keep that in mind if you use both pairs if you go past 75% volume level you could damage the Concept 20’s
If you interested in the spec sheets for your equipment here they are:
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