Apparently it isn't, which means it is likely something other than the interface.

Bernier, did you at any point plug headphones into the 4i4 or the Presonus and check if you then can hear your keys?
At this point we would know they are getting that far. If not, something is probably amiss with the keyboard to interface connection.
Start at the source and work your way forward finding where the issue actually lies.

I do not work here, but the benefits are still awesome
Make your sound your own!