I took apart my keyboard and realized the type of matrix and velocity. Classic matrix and the velocity is double switches per key but both getting contact when pressed just in a slightly different time depending on velocity/force.
Also found a guy who did exactly what I want - connected key matrix of broken keyboard (same type matrix) to arduino. He actually has connected flat cable of the keys directly to arduino mega cuz it has sufficient input pins. As far as I can see on the pic he has even physically connected it directly w/o any additional cables/adapters.
And the code is exactly for velocity keyboards. How cool is that.
I am not sure if it's legit to link that here?