The 3k3y hardware device is an advanced Optical Disc Drive (ODD) emulator, it does not rely on any software based hacks to operate (once the drive key is known).

The device is connected on the SATA (PATA) bus in the PS3, like this; cable from PS3 goes into 3key, cable to BD drive goes out from 3k3y, in other words 3k3y physically sits between the drive and the PS3 mainboard and offers USB 2.0 port to connect hard drive(s). Games residing on the connected hard drive(s) can be selected using a small remote display with buttons (as seen in the photo linked a few posts up reading “PS3” in white characters on the display). You need to open the PS3 to install 3k3y, but no soldering is required.

For the PS3 this device appears as a legit BD drive, and replies to any ATA protocol requests/commands the same way the original drive does. The BD drive key which is unique in each PS3 makes it possible for 3k3y to decrypt/encrypt data on the fly and redirect SATA traffic originally on disc media from the hard drive connected via USB 2.0 instead. No original Blu-ray disc needs to be inserted for operation, you can use this without any disc in the drive.

Again, this makes it possible to use any official firmware (XMB) version you want after installation (and key retrieval). No need for software hacks like CFW or DEX to make this work at all. If the original game requires firmware (XMB) 4.25, then go ahead and update, just like you would if the system was completely original (virgin).

I hope this clears up any misunderstandings what 3k3y does, or what it requires.