I have a Jackson DKMG I bought a few months back that has a licensed Floyd Rose on it.

Anyway, it's really stiff, hard to divebomb, didn't think much of it but today I noticed my whammy bar had bent in towards the guitar from all the use (and I don't even use it that much). Like an idiot, I pulled it up trying to bend it back and the bar snapped (I've done this on my Strat copy countless times and it's never broken). I checked the back and there are only 3 springs, I'm using strings gauged 9-46

My question is what could be the cause of the tremolo's 'stiffness'
Your spring tension might be too high. Try using only two springs.
Agile Ash RB 828
Schecter C-7 (old 90s style headstock)
Handbuilt 6-string V
Handbuilt Baritone scale 6 string Iceman-copy
Pod HD300
Yeah, take one of the springs out definately! I have 10s on my guitar and I still only have 2 springs in, I had 3 in to begin with and it was stiff it was ridiculous so I took one of them out.......although that does mean you have the hassle of rebalancing the bridge, do you know what you're doing there?