Xperia Z2 Won't install rom's
Alright, so I found the solution and it was all to do with my own incompetence.
I was flashing on the wrong recovery, instead of the recovery for the Xperia z2 I was putting on the Z2 tablet recovery. Hence why the recovery mode was detecting "Castor" instead of "Sirius". Flashing on the right recovery immediately solved my flashing problem and now I'm running CM12.