Sounds like you have a good bit of equipment. I love squats, but I would sub in hacks, and it would look like:
Leg Press - 2 warm up sets, 15 reps, very light weight
5 sets (10, 8, 6, 4-6, 2-4) of med heavy working to very heavy
Hack - 3 x 20 of medium heavy
Leg Extend - 3 x 50 light
This will put you on your ass. I don't always do this much, but it was my leg day this week. (I tend to change a lot.) I also will sometimes go with a couple of supersets of curls and extends with med weight, then something heavier, leg press or hacks. Also, I like to do leg press before squats. I feel like wearing out my quads on the press helps me hit other leg areas with the squats.
What about lunges? I personally hate them and won't due them, but you might think about adding them. Also, can you do dumbell squats? Lighter weight and less back stress, but still can be pretty intense with high reps.