Animation, quaternions, ease out movement

Hi,

I'm animating now a character. Rivat from Wayne’s course Animation workflow & body mechanics. While I know I could ask Wayne directly, it seem to me a more general concern for animators and so I thought it would be more appropriate to ask the community.  
... Anyway, I have a problem with the quaternions rotations.


I have to uses some quaternions, even if most bones are in Euler rotations - quaternion is the only solution that allows me to express, to impose my vision on the rig. so far so good... the problem it’s an animation… i.e. when I get into the extrapolation, that is, the Graph Editor, I’m helpless. I don’t know how to manipulate the curves.

I looked at some forums and some tutorials but didn't find an answer. While some helped me to inject some logic and order into the concept, I still don't understand how to manipulate the curves in the graph editor. 

I'm not afraid from a tough learning, mathematics and so, I'm not upset because it's not an easy learning (ok, very upset, but c'est la vie...) I simply didn't find sources that could help me apply it to Blender/graph editor. If you have a reference advice, please share. 


In my animation exercise, I wish to ease out the hands movement at the end of each bounce/move of the character - for 4-6 frames to rap the movement. As if it the hands were a bouncing ball at the end of its up movement. In Euler terms, I wish to create a concave curve of the Z axis but with quaternion.
I enter the Graph editor and clean strange curves but I cannot do much more.

A relatively workable solutions would be:

1. to key frames the hands 4-6 frames before their end movement, so I can have more control on the movement.

2. to tweak the rotation curves in the graph editor, so they perform what I want - though this is trail and error and varies for each movement. That is, I randomly play with the curves and hope some tweak would gives me what I want. 


Then, I wish to avoid these options. Even if in this case, they could be the easiest and the quickest, they are rather arbitrary so they don't help me to learn... which is the reason I'm doing it.
Moreover, it is chaotic. If I wish to fix it later it would be hard to remember what I did. I also wish to create work habits that would enable me to pass a given file to others... to collaborate with others... some day in the future - so the others can exchange with me according to clear referential. I wish to avoid ad-hoc solutions. 

In simple words, I'm banging my head against the wall...any input? and many thanks for the consideration.

DB