After unlocking, I started with flashing stock-17.1.1.A.0.402-sirius-repack.img from http://techerrata.com/browse/twrp2/sirius and was able to get to the new recovery ok. I then proceeded to flashing superuser. After flash and reboot I tried installing busybox but the install failed (, I got the superuser prompt as expected but install still failed. Xposed framework also failed to install with error about not being able to write to system. AdAway also couldn't write to hosts file.
Then I flashed Doom's CWM-Based Recovery 22.214.171.124 from http://forum.xda-developers.com/show....php?t=2702001 and everything started working.. busybox/xposed/adaway installed fine etc.
Why couldn't I install the above when running TRWP?