Need help unbricking my Honor 6 L04

So after more or less randomly trying different things, and fearing that I might only have made matters worse, I hope someone can help:

I have got a Huawei Honor 6 H60-L04 (bootloader unlocked and rooted) and was, until two days ago, running KitKat with the B114 build and cwm recovery. Since Marshmallow has officially benn available for the Honor 6 for a while now, I decided to finally update.
I flashed stock recovery and updated to Marshmallow build B820 via update.app on sdcard. Booting worked fine, however I was unrooted (ofc) so I decided to flash SuperSU (2.76 [latest stable]).

So I flashed twrp 3.0.2.0. and so far all good. Still no problems booting. Then I flashed SuperSU (according to twrp successfully) and rebooted, just to find myself stuck on bootscreen. That is not the first one you get in bootloop but the animated honor logo. Well ****.
Since then I tried many things, wiped multiple times (data is unimportant, but unfortunately I don't have a working twrp backup, please don't lecture me on this, i know -.-), flashed almost any stock ROM I could get my hands on. In twrp I get this Error:

Could not find 'META-INF/com/google/android/update-binary' in the zip file". >"Error installing zip file". "Failed"

Somewhere on the way I got

error! Func NO : 9 (FUNC_BOOT_KERNEL) Error NO : 2

while booting, that's gone though.

I'm at the point now where I can install B820 via update.app on sdcard, see the installation progress succeed to 100%, reboot, and again, find myself stuck on animated honor logo.
I honestly have no idea what I can do, I hope someone here does. I'll happily provide any further information you might need.