Whoah!
Thanks for the feedback chaps. My mistake - I was referring to the 'AUX' port all along - it's not marked 'expansion' at all - nicely sussed.
@ Speelgoedmannetje - since you've made a cdtv-to-cd32 keyboard adapter - does this then mean that the cd32 has all the necessary keyboard controller circuitry on the mainboard?
If so, do you think it likely that a PS2 keyboard adapter (i.e. the IBMKey design) can be hacked to work with it?
Thanks again.