Android 6.0 M (MPA44I) Preview 3 got Root but no R/w to System

HI

I´ve rooted my Nexus 6 on MPA44I

1) twrp-2.8.7.1-shamu
2) BETA-SuperSU-v2.49
3) Despair.M.Shamu.R6.4.zip

but i can´t use apps like Adaway , its saying "can´t create /system/etc/hosts: read only file-system"

Root Checker says "got root"
Titanium Backup works

how can i get full Access to stop these anoying ads?

thanks for your help