fn+brightness not working on windows 8.1 on M6600

Hi. Thanks for any suggestion or advice you can provide.

I have been using Windows 7 on M6600 for a while. it mostly worked besides I was getting "Nvidia Kernel Mode Driver has stopped responding and has recovered issue" at times and I had no choice but to reboot to make it work again, that is for a while...

When windows 8.1 became available via corporate, I got hold of it and decided to reinstall fresh. 

I saved all my data and wiped out windows and recovery partitions, leaving dell system partition.

Windows 8.1 install was amazingly fast, 15 mins. As soon as I booted I installed Dell chipset driver, video drivers and other drivers. All device manager entries were with no warnings, some drivers were found and some I installed from Dell site. I installed most critical programs and all was cool and working. Nvidia video driver crash seems to be gone too. I have 2 other windows 8 machines so my windows 8 experience was there and I am quite happy with everything in windows 8.1

Then eventually I noticed that LCD brightness does not work. I made sure I had Dell Intell HD 3000 driver, Dell Nvidia driver and Dell feature pack installed. I tried with Dell feature pack and without it.

I researched this topic, found some other reference to Windows 8 having the same issue. I do have 3 monitors and do run Optimus. this all worked very well in windows 7.

Some posts suggested that it is critical to install drivers in order. I started doubting my install process, if I missed anything. I created system image of what I already had rebuilt in windows 8.1, and did full clean re-install. when windows 8.1 came up, I was always checking brightness. I was working fine using windows 8.1 native control. It popped brightness window and moved up and down, adjusting brightness. I immediately installed chipset driver, rebooted, noticed that windows installed its generic Intel HD 3000 driver in the background(which broke brightness), and right away on the top, installed latest DELL Intel video driver and rebooted; brightness control still broken. This all according to Dell reinstall guides. As soon as windows found HD 3000 and installed driver, fn+brightness stopped working. so regardless of any other drivers, Intel driver kills it and dell Intel video driver does not restore brightness control.

I tried this again. Format partition and 15 mins later, repeat of story. As Intel video driver gets installed, kills control function and Dell Intel driver(Win7-8_64_15.28.14_3040_Dell_setup_ZPE) does not restore it.

So I restored windows 8.1 saved image to get my first windows 8.1 rebuild. BTW, those that install 8.1 don't need to use Dell security software(DDPA_Setup_TDC1K_A06_64bits_ZPE), windows 8.1 supports fingerprint scanner by default. just configure it. it works great. 8.1 is vey snappy in my laptop and I like it. I boot to desktop(not using Start 8, which I use on win 8 machines) and MS start screen is an OK compromise in my opinion.

This issue has nothing to do with install sequence here. chipset and video drivers are installed in correct order by me.

I can control brightness going in and using BIOS. but that is ugly way. I can control brightness while windows 8.1 boots, which is quite fast on M6600 with SDD drive, but it requires reboot and hard to judge brightness at that point.

Some suggested that it's due to Optimus. I need it, as I use 3 monitors and travel at times. and it worked fine in Win 7.

Any of you have any idea what else I can do? Thanks a lot for any suggestions!

P.S.I found the following reference http://adrynalyne.blogspot.ca/2012/10/fix-brightness-control-for-windows-8.html which seems to suggest that it might be deployment issue.

My Windows 8.1 install with Dell Intel driver shows "FeatureTestControl"=dword:0000f960 currently.

Could anyone post what is their Windows 7 registry value for FeatureTestControl is using latest Dell Windows 7 Intel driver, please?