Was it hard to install the dark rock 3? I'll be Installing with the motherboard in the case.
Dark Rock Pro 3 - I have, as you notice there is a difference
Hard to install? No. And I will recommend to do it like you do - mobo in case
Backplate first. Then you have to fit four screws from back, blocked on front side of mobo with plastic clips, so they and backplate stays on place no matter what.
Stand the case vertically with front towards you, grab the cooler in left hand, with AMD / Intel brackets fitted already and move it towards CPU.
Locate bottom holes of brackets against screws coming out of mobo until touch them, then slowly rotate cooler until touching top screws. While keeping like that carefully screw them with right hand, from backside with screwdriver like nearest top one till catch thread, furthest bottom one, furthest top one, nearest bottom one like first one - and rotate on them after some screwdriver turns to prevent overtighten one corner before tight rest of them
Now to make it funny - that is really sounds way more difficult from that how it is going
Hope is that helps
Digipact, sorry - correct me if I am wrong - instead of that Intel CPU 'holder' with hinge fitted by three holes (sure this is called somehow) which locking CPU in place - you've got some retention module? I think I've seen that the other day - and you right about it. If that three holes mentioned above are on mobo that is the solution, if not you have to do your way unfortunately... If that three holes are present - there's no problem as at least the solution is available.
The thing is, at least most of CPU cooler manufacturers provides the backplate fitted to the mobo by these holes - it is not only be quiet! issue...