Yes, there is no analog touch sensitivity on the sax: keys are either open or closed. The pressure sensor is for volume and note attack.
Razer has keyboards with optical ones, and some people have made them by putting inductive sensors underneath mechanical switches, but I couldn't find any analog keyswitches for sale. Do you have some examples?
How can you deal with a large number of analog inputs to a Raspberry Pi or similar?
But the full design is published, just in case anyone wants to try :)