So I got home from work and did this....
Using the gunslinger class, make sure your agility is maxed out and you have the "Higher Jump" selected. having a weapon equipped with a +2 agility perc is helpful.
Make sure you jump off the rock as the weight of darkness is disappearing. Time it and hold X on your second jump to ensure the maximum amount of height gained from the jump.
It's been done with warlocks and titans as far as I've seen. Hope this helps for the Hunters out there.
Here's my second video that shows the rest of the abyss part
http://youtu.be/J-g-gsyHS6M
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Man, I've been trying this for the past 3 days and have put about 5 hours into this. I absolutely cannot make the jump. I have everything set up correctly and still cannot jump high enough. High jump/max agility/gun with +2 agility and holding the jump button down. Watched the vid like 30 times, guess it's just not going to happen for me.