I found the buttons very hard to press, and quite noisy.
I think this is the ones you are using:
The datasheet says the operating force is 260gF. A normal keyboard is around 50gF, gamepads should be roughly the same. The lightest in the same series is 130gF. Not ideal, but it should be much better:
Here is the complete datasheet: http://www.omron.com/ecb/products/pdf/en-b3f.pdf
I will eventually try these other pushbuttons. I’ll have to unsolder the others without damaging the board though. Wish me luck.
I cannot find the same round caps. What is the refs?