If you just want to use the DK control panel, there's nothing to it. The terminals on the microswitches for the DK joystick and buttons are standard .187 quick-disconnects, and the wiring included with any of those cheap Chinese USB joystick encoders will fit onto the DK switches (though they sometimes include the smaller type QDs for Sanwa-style buttons). You can get one of those USB encoders for like 10 bucks (IPac is overpriced and sorta outdated).
There's no way to use the original DK CP wiring harness to connect to a USB encoder without unwiring it from the two original connectors and replacing with connectors that will mate with the USB encoder. But there's no reason to do that anyway, since the encoder will come with the wiring you need.