Hotshotz, I'll try to explain it to you as best as I can.
The reason that some say that you need a CK3 lite/ pro, is because using an external power source to power the drive, is the only way to power the drive, without the console being able to register that it has been booted up without a dvd drive.
The Ck3i/ Lite or Pro are all units which are used to power the dvd drive from an external power source. That means that when you are using the Ck3 device, you also need a power source. This can be your computers internal power supply, or you can buy an external power supply to connect to the CK3.
Now, some people say that it is sufficient to just use the xbox 360 console itself when you are powering the dvd drive, while you are flashing Custom firmware to it.
However. Some people say that when you do this, the console itself registeres that it is being powered on, without the dvd drive connected to the sata port on the xbox 360. The console can then send this information to Microsoft the next time you connect to live and the console can then be banned from xbox live at a later time.
But I have read a lot of different claims, where some people says this isn't true and others claim it is. So take from this what you want.
But I would say, if playing on xbox live is important to you, then go for the Ck3.
As for the X360USB pro. This is used only for connecting the dvd drive from its sata plug to your computer. The X360usb pro communicates with you computer through usb cable and passes the signal on to the dvd drives sata connection.
The VIA 6421 Pci card, supports some of the xbox 360 dvd drive models, but not all.
The X360usb pro, supports all drive models. So if you choose the x360usb pro you can't go wrong.
Now for the Probe 3. This is ONLY needed if you have an old version (Phat xbox 360) Liteon drive. So if you have a hitatchi, samsung or any of the other (including slim drives) you DO NOT need the Probe 3.
The probe 3 is used to grab the key from the old Liteon drives and it can be used, whether you are using the CK3, or if you are using your xbox 360 console for powering the drive.
But again, for "safest" possible way to play on xbox live, I would recommend that you use an external power source, instead uf the xbox 360 console as power source.
This post has been edited by oleq83: Feb 7 2012, 06:52 AM