[Xperia Z2 Tablet Q&A, Help & Troubleshooting] Elliander:
I tried using Towelroot on my Z2 Tablet (SGP561; Build: 17.1.D.0.417) and it said it was successful, but I couldn't get SuperSU or Superuser to work no matter what I tried (and I previously had success rooting other devices) so I am assuming at the moment that it gave me a false positive on success.

I tried a few other methods each without success. Cyanogenmod doesn't support it and neither does "Safe Root". I did appear to have some success with Motochopper n7, but when it failed to reboot the device (didn't give me an option to do it manually) and then cleaned up.

Manually rebooting the device after it finished resulted in no improvements, but trying the Motochopper exploit again indicated that it recognized a previous rooting and so it failed for that reason:

[*]
[*] Motochopper: Android root exploit (Windows version)
[*] v1.0
[*] by Dan Rosenberg (@djrbliss)
[*]
[*] Tested on the Motorola Razr HD, Razr M, Razr Maxx HD, and Atrix HD.
[*] Supports lots of other devices as well. ;)
[*]
[*] Before continuing, ensure that USB debugging is enabled, that you
[*] have the latest USB drivers installed, and that your phone
[*] is connected via USB.
[*]
[*] WARNING: This will likely void the warranty on your device. I am
[*] not responsible for any damage to your phone as a result using this
[*] tool.
[*]
[*] Press enter to root your phone...
Press any key to continue . . .
[*]
[*] Waiting for device...
* daemon not running. starting it now on port 5037 *
* daemon started successfully *
[*] Device found.
[*] Pushing exploit...
2109 KB/s (1283460 bytes in 0.594s)
[*] Pushing root tools...
1952 KB/s (91980 bytes in 0.046s)
2296 KB/s (1867568 bytes in 0.794s)
2446 KB/s (969701 bytes in 0.387s)
pkg: /data/local/tmp/Superuser.apk
Failure [INSTALL_FAILED_ALREADY_EXISTS]
[*] Rooting phone...
[+] This may take a few minutes.
[-] Failure.
[*] Cleaning up...
[*] Exploit complete. Press enter to reboot and exit.
Press any key to continue . . .

Of course, root checkers say the device isn't rooted, but on my towelrooted phone it says that anyway unless it is given super user privileges, so I have no way of knowing if it is rooted or if it isn't. I am inclined to believe that it isn't though because TA backup fails:

[ ------------------------------------------------------------ ]
[ Backup TA v9.11 for Sony Xperia ]
[ ------------------------------------------------------------ ]
[ Initialization ]
[ ]
[ Make sure that you have USB Debugging enabled, you do ]
[ allow your computer ADB access by accepting its RSA key ]
[ (only needed for Android 4.2.2 or higher) and grant this ]
[ ADB process root permissions through superuser. ]
[ ------------------------------------------------------------ ]

Waiting for USB Debugging...OK
Pushing Backup TA Tools...OK
Checking for SU binary...FAILED
Requesting root permissions...FAILED

=======================================
CLEAN UP
=======================================
Deleted file - C:\Users\Elliander\Desktop\Backup-TA-9.11\Backup-TA-9.11\tmpbak\r
ootPermission
Deleted file - C:\Users\Elliander\Desktop\Backup-TA-9.11\Backup-TA-9.11\tmpbak\s
u
Removing Backup TA Tools...OK
Killing ADB Daemon...OK

Press any key to continue . . .

I actually do want to Unlock the boot loader, it's just that I want to back up the DRM keys first. My tablet it already unlocked to be used with any carrier, but I think it's ludicrous that these types of restrictions are allowed on such expensive hardware. At the very least Sony should officially have a tool to backup the keys when unlocking so that it can be restored to the same device.

EDIT: When I looked in:

About Tablet > Status

On the bottom under "Rooting Status" it says "Rooted"

So I'm guessing my only problem is in getting the Super User binaries to work?

EDIT 2: BusyBox Installed (from Play Store) also says my device is rooted, so something I did in the above worked. Unfortunately, the install of Busybox also failed.