Grumpy_Mike:
wvmarle - not sure what you mean by the keys producing an analogue output.
Pressure sensitivity can not be a plain 1/0, on/off kind of signal.
It could be a double signal (based on the speed the key goes down, rather than the actual force that's applied, that needs timing - two switches that get triggered one after the other as the key moves down), it could be a pressure sensor which returns an analog voltage (it sounds like "aftertouch" is doing something like that).
Unless I totally misunderstand how those keys work - and then I'd like to hear OPs comment on their exact working.