I was just commenting about the fact that cm13 would not flash, even after checking that partitions were not on read only as RBS01 indicated.So flashing from Omnirom 4.4 doesn't work huh...
Re-stock and flash it again, then, flash Omnirom 6.0. If a warning shows, ignore it and flash it still. Once Omni 6 is installed, wipe the following:
/system
/data
android.secure
And then flash CM13
In fact I did not yet try to flash from Omni 4.4, I may stay a while like this