All of these comments should be taken at face value, you’ve gotten some good advice, and here’s mine.
Basing my observations off this video http://www.youtube.com/watch?v=18bqEltu1as (since it’s about the clearest view of a heavy squat you have)
-Widening your stance isn’t gonna keep your more upright. The opposite will probably happen.
-I would say your grip is too wide. If you can bring it in some your upper back should tighten up alot. This has worked well for me and several others that I train with.
-After you walk it out, and before you even start the squat, pick your chest up. It’s a hard concept to explain, but imagine your were standing with a bar across your back, try to pull your chest up high, like if you were puffing it out on the beach. You should feel your upper back arching. Before every rep on every set, make sure you’re picking your chest up. It should keep you more upright on the way down.
-When you’re on the way down, and before you reverse out of the hole your head is dropping and upper back seems to be caving some what
-Keep driving your elbows forwar hard as your hit the hole. Make sure everything is tight and drive your elbows forward hard. This should help with the above point since it’ll keep your chest up and your upper back arched
-When you hit depth you seem to get kicked forward. This could be because you’re descending too fast, and once the suit binds up you’re being kicked forwards, or you’re not keeping tight enough.
Just some thoughts and suggestions to consider. They’re actually something someone much more knowledgable than I suggest to me a good while ago and they worked well for myself!!