Get the Dell premium tower cooler for XPS 8940 which will fit 8900 cpu socket like a glove.  User has reported good performance and quiet operation.
I am using an older XPS 8900 mobo for an unpaid build.  It has an Intel i7-6700 3.4 GHz. Everything is up and running fine but the fan is loud.  So I took a look at the fan mounts and of course it has the Dell supersize holes and I don't have any backplates that fit this.  Also, the CPU mount screws into the back bracket so if I replaced it then I would have to stick some nuts on the back of the board to hold the bracket in place? Does anyone have any recommendations on a quiet cooler that works.  Space is not an issue - it is in a large rack mount case.  Thanks.
XPS 8900, LGA1151 cooler upgrade recommendation