The usual Alienware supplied OS license will die as you change to a non-Alienware motherboard. Why not save 100 bucks for the OS and find a good working Alienware board?
If I was to tackle this I'd check out motherboards at https://www.google.com/search?q=best+ddr3+i7+motherboard+tomshardware and see if I could use any boards at
https://www.reddit.com/r/PCMasterRace/wiki/builds
I had an Alienware X51 R2. I was having an issue with the screen shutting off in the middle of gaming. I looked around on various forums and found out they have heat issues. I decided to scavenge the parts and put them into a larger tower. Unfortunately, I cannot make heads or tails of the motherboard, so I need to get a new one.
So the components I have are:
2 8G DDR3 Ram 1600 MHz
Intel Core i7 (4th Gen) 4770 / 3.4 GHz LGA1150 Socket
nVidia GTX760 Ti OEM
I need a motherboard that can utilize these components and still be able to be upgraded later with 2 better video cards and more ram. Any recommendations?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic