I have just rooted my Samsung Galaxy Tab S SM-T800 and I tried [ROM][6.0.1][UNOFFICIAL][WIP] ResurrectionRemix- SM-T800
Anyway it didn't work as I would like it ie = no camera wouldn't recognize my mico sd card, so I tried to revert back to stock firmware via this tutorial https://theunlockr.com/2014/08/09/how-to-unroot-the-samsung-galaxy-tab-s-10-5-wifi/
I have downloaded odin and firmware for New Zealand and gone through the procedure.  The only way I could get into download mode was plug in the Samsung plug that enables it into download mode once turned on.
And after trying to flash stock firmware its just stuck in boot mode and I can't turn off and can't remove battery, so let it go flat overnight recharged.  And retried and and I'm still stuck in boot screen.
Any help please!

it may well be that you need to boot into download from power up, should work does on my note 10.1. Try again and see what Odin says when it is finished. 

Thanks guys but I can only let the battery run flat recharge and the plug in Samsung Galaxy S Download Mode JIG to enable me to get into download mode, if I try power button it goes to frozen boot and the three buttons will not work!

So I have to wait another 24 hours and try again!  hope this makes sense.

Android version 5.0.2
I have sorted my problem with stuck in boot screen downloaded UK firmware and it loaded OK, the other NZ ones were missing MD5 what ever that was!
Anyway managed to get into recovery and then finally it loaded the UK firmware now back to stock.  should have left it with the Nova launcher and it behaves better than all the Samsung splash screens which I don't like.
I did find it awkward trying to press the three buttons on a tablet with my 74 year old fingers.
There doesn't seem to be as many roms available as phones for this tablet might look for lollipop 5.1.1