Windows 2008 R2 on DS6100?

Possible?  Sure

I would really recomend taking out the 2 system drives and inserting another 2.5 drive with to play with.  They are cheap enough and you would be able to fall back to the original if you need to.

Fans will blow full speed without the WD software.  and if you load 2012 you will have storage spaces for the 4 drive bays.