I own a Technics KN5000 and recently spent some time trying to find a Win 2000 driver for the PC to Host Port feature.
Well, as per usual, manufacturer and reseller support was not forthcoming, so i just went ahead and tried a few things myself.
It seemed obvious that the cable required was a standard 9pin serial to 8 pin DIN serial cable - I had a few around from various pieces of equipment, but they should be readily available.
If it was standard, then seemingly a standard Midi to serial would also work!
I just installed the Roland Serial to Host Driver (available from their site) and it worked perfectly.
I would assume the case would be much the same for other keyboards with this feature.
Regards
Klaus