It is most likely down to a simple dword. I had a brief look at the inf but nothing stood out at first glance. Use a registry snapshot tool to create a "snapshot" of a working config (VGA_AMD_Win8_64_VER900300000.zip) and a non working (newest WU driver) - compare snapshots to find the odd dword. Check your PM for a tool.
Many would wish for it to work like that but that isn't quite the way PXAI devices work. There are some older fixed switching based devices for whom this method works on a BIOS level since a MUX chip exists within the laptop. Newer "non MUX" chip laptops have to route the AMD signal through Intel to the displays... so turning it off is not an option. There is a fringe method but it includes modding the BIOS.
In this case you will need to try one of my modded Intel drivers that redirect the internal video passthrough. It was initially made for fixed switching with a patch to restore backlight upon LVDS switching. Clean with DDU in Safe Mode. Install an Intel (Modern) driver from the UnifL 14.4 2.2 package then Install either the latest official AMD driver from AMD or from WU.
This has something got to do with the wrong installation of my Application Unlock (the files I sent you). Essentially I prefer bundling it with our UnifL releases as less mistakes are bound to happen. Are you sure you applied the files properly and into the right directory? Note that the directory of CCC (mentioned in the readme text file) changes depending on if you are using WindowsUpdate AMD drivers (CCC2) vs Official AMD drivers. This fix is made for the WU version. You have to make sure to delete the *.bat file (in C:\AMD) then kill CCC.exe via taskmanager and overwrite the files. (or overwrite them in safe mode - easier) Otherwise it looks like a fully working driver. You just need to fix this. Indeed. The 6470M and 7400M is the same card. The later is a rebrand and the driver cares not for being precise with names.
Hehe Asus.... in your dreams ; ) Try this. Once AMD from WU is installed .. uninstall CCC only. Also make sure to remove C:\AMD as it houses a *.bat file which runs on every start forcing CCC to reinstall. The reason I am asking this from you is simple. You receive the backlight issue after you see the login screen for a tiny second. This means that during the boot process, CCC or a part of the AMD driver loaded and is preventing the backlight from working. So either CCC is at fault or the driver itself. Try to find out!
FIrst rule is to never ever install via the auto tools....they are utter junk ; ) The 7400 is a rebrand of your card. The name is not important and does not have any negative impact on the functional. So Windows Update does not load any drivers at all for your AMD card? .. very hard to believe.
Have you tried cleaning with DDU in safe mode and then seeing if Window will autoupdate the AMD drivers: http://www.wagnardmobile.com/forums/viewtopic.php?f=5&t=15 ? Intel should autoupdate to 4229 I believe.
Am not sure if I understood the issue at hand. You are currently on Windows 10 (upgrade from 7) You have an Intel HD 3000? + 6470M PXAI device. The drivers work but your internal laptop monitor will not show an image unless you plug in an external monitor. In that case the internal and external both display the same picture? You tried the stock Asus drivers on Windows 10 and they worked? Seahorsepip already mentioned that the UnifL drivers we provide make most of the changes to the dwords in the inf files in both the Intel and AMD driver. They might help but if you give me more info .. then I might be able to look into it.
The answer might be simpler than you imagine. Your OS language and location matter a lot. It can make or break Cortana and enable just Search. So if you have a strange mix match of location and languages then it might tell you that not even Online Search is supported in your region.