I played thru a Suma 300 yesterday...I didn't like the sound or the overall volume..I think the output is overated..
Next to it was a Behringer 1200..It was louder at half volume than the Alesis[but no effects]..The new 1800 might be worth a try..

Do you think that 2 of these KX1800, one on each side, will be enough for a 150-200 persons room?

The KX1800 shows an output of 180 watts.
I would think that 2 would be MORE than enough.

Over the years, I played many jobs with audience size in the 150-300 person range.
I would use 1 200-watt amp. At times I would be asked if it was possible to turn the volume down a little...
but never was I asked to turn the volume up!!

But maybe that had something to do with my playing.

So, Two of these can be an alternative solution to a standard PA system.
Now, we have to wait for the detailed specifications