Yes, using a Z620 cable and an add-in card to provide USB 3.0 to the front panel of a Z600 is exactly what I am trying to do. I would use an add-in card and a 5.25" usb 3.0 add-in "bay" but both of my 5.25 slots are currently filled with other peripherials. I was going for a "clean" look and trying to see if I could swap out the cable assembly and use the 20-pin USB 3.0 connector on a add-in card to drive the USB 3.0 ports on the front of the PC. Now that I see that, due to the cable length, the assembly has a redriver that needs 3.3V power, this has become even more of a challenge. I am well versed in electronics, so it would not be difficult to use a 5V to 3.3V converter to step the voltage down off of the 5V rail from either the power supply (preferred) or a 5V connector on the mainboard. Sounds like a interesting project to tackle. The easy route would be to free up a drive bay for a USB 3.0 interface (such as the Akasa that SDH reccommended), but I think I like the idea of tackling an actual electronics project. I can break off the two 3.3v and ground pins from the USB 2.0 cable, and then use the remaining pins to connect to the USB 2.0 motherboard header to provide the USB 2.0 service to the front panel. After that, it is just a matter of getting 3.3v and ground to the USB 3.-0 redriver from a stable source.
I appreciate all the info and advice given, and I will post back when I have figured out how to do this.