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 9 pin 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.