My OB6 Desktop also responds to aftertouch (from an Oberheim Matrix-6 used as a MIDI keyboard controller). Mine isn't as sensitive as Chimponaut's (my Matrix-6 aftertouch control is very gradual). And, of course, the OB6 desktop will not send any aftertouch signals by itself. It needs to receive such MIDI data from a MIDI aftertouch equipped keyboard.
BTW, as I said before, all the knobs are rock solid on my OB6 Module.