I believe they started adding root from 108k4 onwards. Try the 107k4 firmware
http://www.mediafire.com/download/k3j33s7tchtfrsf/M82_107k4_sdcard.rar
It looks like they started providing root access with 107k4, any chance you have 106k4?
109k4->
1.Optimization Power Consumption.
2.Improve stability issue When auto reboot,auto suspend,Monkey test,AV file continue playing.
3.Add protocol: UDP ,RTP , MMS ...
4.Update NAND/EMMC driver.
5.Fix some Wi-Fi throughput problem.
6.Support Antutu videobench apk.
7.Optimization display effect for HDMI.
8.Support new feature DRM,Playready L1/L3,Widewine.
9.Add Secure OS.
10.Visit America websit netflix and youtube smoothly.
11.Strengthen encoder stability.
12.Change the Mxplayer to normal version;
13.Update xbmc to Gotham 13.2,and open some nodes' authority,so you can install any version of xbmc;
14.Make the physic power-key to be suspend/resume working by short press,and long press (5s) to shutdown;
15.Remove the Popup notification when xbmc/Mxplayer/... been ran at the first time;
16. Add an Icon to show/hide Status Bar;
17.Support Hausbell Mmini i8 and Rii Mini H7 air-mouse;
18. Make some portrait APPs to be showed to landscape,such as Antutu;
19.Fix issue:the A/V Async for MPEG2;
20. Fix issue:it may auto-wakeup when in suspend state;
21.Fix issue:the usb port may lose efficacy after resume;
22. Fix issue:no sound for Notification;
23. Improve some parts of MBXLanucher;
24.Fix issue:Google Calendar/People cant sync.
108K4->
1.Add 1080P24Hz support;
2.Support for NTFS/CIFS; --Offered by wasser
3.Change Input method to Latin,and remote can use;
4.Update Play Store;
5.Support for Mele F10 air-mouse; --Pulled from Bob's FW
6.Support for Xbox/PS3; --Offered by Bob
7.Change method of Root access; --Offered by leolas
8.Add kill-recent-task function; --Offered by daemonium
9.Update xbmc to Gotham 13.1,fix 4k playback and 2160P/720P HDMI display issue; --THX stane
10.Add remote function in Recovery Mode;--THX leolas
11.Adjust MBXLauncher,add Yahoo wether and Clean-Memory function,fix slow animation issue;
12.Fix issue->Power-key of Remote might lead to reboot;
13.Improve small probable of blurred screen.
107k4->
1.Add for CPBLTV live stream;
2.Decoding Dts/Dolby for S802;
3.Add suspend and Power-off function by Remote or power button from Status Bar;
4.Add root access permission.
106k4->
1.Enhance system stability;
2.It can flash Ethernet MAC;
3.Enhance the power of 4k video decoding;
4.Fix issue of 1080i video playing.
105k4->
1.Fix some LiveTV apk can't be ok;
2.Optimize Thermal control;
3.Optimize HDMI/AV;
4.Optimeze Launcher/Settings,use only 1080P UI;
5.Fix video burning test fail;
6.Support secure OS function;
7.Update NAND driver;
8.Support APK installation to external SD.
103k4->
1.Better xbmc for playing 4k video;
2.6210_8G compatible with 6330_16G,to be the same FW;
3.Add PPPoE;
4.Adjust thermal control,Special for Antutu;
5.Adjust HDMI signal to more TV compatible;
102k4->
1.Better xbmc,no async between audio and video ;
2.Fix 5G wifi compatibility;
3.Better for Antutu benchmark;
4.S802/S802B/S802H are all compatible;
5.Other little tweaking.