Funny, how people are looking to root their device but re-think about rooting it. Don't even think of rooting your phone if you're unsure about what you're doing. Might as well just buy an iPhone and forget about modding your phone to its full potential.
Seriously, I don't even give a damn about warranty and DRM keys. I bought the phone, and it's mine. I should have full control over it and modify it as I want, say unlock the bootloader or whatever it is, hey it's my money well spent why should I care less... The only problem that will come in is when you put your Z5 premium dual into water and it starts to evaporate on your camera lense then you should send it to Sony for warranty or just send to any mobile phone shop and spend some money. Come on the moment your warranty is over, your phone will become obsolete, Z7 will come in hand.
Edit: Anyway, enough random rant. If you still wanna root your phone check this out for the DUAL variant...
http://forum.xda-developers.com/z5-premium/general/complete-noob-friendly-guide-to-t3426220