If you're using iPrep to flash a BenQ or Samsung you only need VIA 6421 controller card or OnBoard Sata that is compatible.
If you're flashing a LiteOn, you will also need a COM Port on your computer to get the drive key using the RS232 cable that comes with the CK3 Lite.
The com cable needs to be plugged in when getting the key, inquiry, and such files, but is not needed while flashing. Most people do the dump and the flash in a single process so the com cable stays connected. But you will need the com cable for at least the dump of the drive.