[HELP] Installing Linux together with Windows 8.1 on Alienware x51 R2

Well here comes the story how I've installed GNU/Debian-testing on my brand new DELL Alienware X51. Google is not much a helper here. So better read this down to the end before you attempt to destroy your PC completely along with all the data you have on it.
 What I did was re-partition available SSD/HDD into the most convinient way. As I had 256GB SSD and 1TB HDD choice is quite obvious. Cut in halves. SSD first half remains total under Win 8.1 control. Remaining will be used as 2GB swap and  for / partition. HDD last half is given to /home. As "/home users" will join me very soon. All the above stated should be done within Windows itself. Run in opened string type 'diskmgmt.msc'. You'll launch drive management tool. Be very careful at this stage you decide to shrink your Win space. Leave enough to load couple of your favorite games. That will suffice. Next step - to install UNetbootin. For that reason you better prepare USB stick. Mine was USB 3.0. Gosh that was quick installation!
UNetbootin ( unetbootin.sourceforge.net) is a program that runs from within Win. It's mostly self explanatory. In our PC-case we need to install Debian distribution with Testing_HdMedia_x64 flavour. Additionally I've downloaded .iso image ( cdimage.debian.org/.../iso-dvd) which for Alienware X51 should be 'amd64' - testing strict! That image to be chosen as Disk Image for ISO Standart during 'UNetbootin' set up. Then choose FAT32 - formatted USB stick (you've got one right?) and go on with installation of bootable USB. It will take some time. Reboot from Windows with clear understanding that you are about to say it goodbye! (And in some cases to all your files too!) But not this time. Press and hold F2 key. Reboot brings you to initial boot screen where you should desable 'Secure Boot Control'. Along with it 'Load Legacy OPROM' goes disabled. It's OK. Next change boot order for USB to boot first. It will go like 1st-USB Hard Disk, 2-nd UEFI:Windows Boot Manager and so on. With your USB stick prepared by UNetbootin make reboot into USB boot. Debian installation starts in UEFI-mode. If not - start everything from beginning. You've certainly missed something! I won't describe the whole installation process. There's nothing in it except one point. As soon as you'll finish your partitioning and write changes to Hard Drive all your correct and incorrect actions will be curved in stone for ages and you can not reverse it back! I always note down my partitions in hand writing on paper before and AFTER changes are made, but not saved yet. That way you will have complete partitioning table right at your service with all necessary drive letters, partition types and all that stuff. Also you may cancel everything and dive back to Win harbor without saving the changes to installation process. Create 2GB swap, / partition where it should be and don't forget to segregate /home from the rest. It's the way I do it last 5 years of Debian use. You'll see why after another 5 years. Finally complete all the changes and write them on disk. It's crucial step so think trice! After that nothing could save you. During installation you can sit back and relax. My case it took me say 25 minutes or less. And there was no problems with GRUB-loader! If GRUB istallation went right you'll get appointment to boot your new system from last page of Debian-installer. Don't forget to switch back changes you've made to initial screen by pressing and holding F2 during this reboot! Bring back only boot sequence this time. 1-st boot will be UEFI:debian 2nd-UEFI:USB and so on. Upon saving the changes you should get ready to amuse to world of Open Software with Win 8.1 as back up option which I use less and less these days ;)