I followed this blog post line by line and it worked well.
The longest portion is simply waiting for the file to download. The free subscription took about an hour. In case the blog was taken down or moved I thought I'd put it here for future use.
1. Download Android 4.4.2 XXDNA1 Firmware for Galaxy Tab Pro 8.4 T320 from the above list
2. Download Odin 3.07
3. Switch off your Tablet and boot Galaxy Tab Pro 8.4 T320 into Download Mode by pressing and holding the Volume Down and Power keys together until you get the warning message, now press Volume Up key to proceed to Download Mode..
4. Extract the downloaded Odin3.07 zip file and run the Odin3 v3.07.exe file as an administrator (Right click on the .exe file and click on Run as administrator)
5. Now connect your Galaxy Tab Pro 8.4 T320 to your computer via USB cable
6. In Odin3 screen, you should see a COM Port number like “0:[COM7]” at ID:COM section and “Added!” text at the message box. This means your device has been detected by Odin3.
7. Make sure that, only the “Auto Reboot” and “F. Reset Time” options are checked.
8. Now, extract the downloaded firmware zip file, you’ll find a firmware file with extension .tar.md5
9. In Odin screen, click on PDA button and select the firmware file with .tar.md5 extension (The firmware file look something like: T320XXDLJ5_T320ODDDLI7_INU.tar.md5)
9. Now, click on the Start button to begin the installation process, wait few moments.
10. Once completed, you would see “PASS!” message in ID:COM port having green background
Your Tablet should automatically reboot after completion. You can now disconnect your Tablet from computer
You are now un-rooted, running stock recovery and the Android 4.4.2
Hope this helps someone get all the information in one spot.
Oh yeah, Yes your Knox is still tripped. Don't think anybody has developed a fix or workaround for this yet.