Unfortunately, that pinout isn't correct for the XPS 8300. Found this out the hard way last night when trying to do the same thing as the OP.
🙁
There is, however, a pinout guide printed (very small) on the mobo itself. I was able to use that to decipher the layout and make this guide (below).
Note: I am fairly certain that the 2 pins directly below the power button are for a reset button, as is indicated on the mobo. However, because the XPS 8300 has no reset switch, and I personally don't like having one enabled on my new case (Corsair 600T), I chose to ignore it.
Note 2: For anyone wondering, once I figured out the I/O pinout, everything else was cake. I was able to transplant the innards of my XPS 8300 over to my Corsair 600T case with no issues--even the mini wifi card. The only thing I replaced from my current 8300 config was the power supply, scrapping Dell's 460w PSU in favor of a Corsair AX750. It booted up right away. Just make sure to write down what goes where when you are disconnecting the Dell.
The only hiccup I ran into was an error message at bootup telling me the case fan was not connected (because I used the connectors on the Corsair case, instead of plugging them into the mobo). In hindsight, I will probably move the rear exhaust fan connector back to the mobo so I don't get that error every time I boot up, and leave the top/front fans plugged into the Corsair controller.
This is a work-in-progress for me. Next stop: new video card! Currently using a GTX 560 -- upgrading to a 660 Ti shortly.