Damn, you are confusing my old man brain here!
You originally started this thread saying your goal was to get a more defined "6 pack" but now you're talking about "beefing up quickly" and taking crash weight gain powders??
Now not to say that those 2 goals can't ever be friends BUT it is starting to sound as though you ain't too sure what your training aims and goals are?
May I suggest you take a timeout from looking at powders, sit down and write down a personal target for yourself...
E.g. "I want to put on 10kg on lean muscle by the end of the year" or "I aim to reduce my bodyfat by 5%" or "I want to be able to squat twice my own bodyweight" or WHATEVER your goal is.
THEN you can investigate and research what you need to do to attain your goal.
(ps: no point asking me anything about mass mixtures and weight gain powers and all that malarky, I'm old school - I like REAL FOOD! If I need to gain weight, I will eat MORE REAL FOOD! Simple eh?! LOL!!)