Your gains on gear, just like when natural, are all going to depend on your diet. If you only gained 6 lbs on 500mg test and you are newer to gear, you are probably not eating enough. Even if your trainig was sub par, you should gain more than that. I would expect at least 15 lbs of gains for a first timer. Most people dont really understand how much we really have to eat to grow and stay big. There is no mystery to how we do it. We are eating several times more than what your normal person would call "a lot" lol. This is where the real work comes in and this is the reason that 99% of people in the gym aren't big ripped bodybuilders, even when they've been trying to be for years. 

Start with protein. This is the most important macro. You want to use whole food sources over whey supps. Chicken eggs, beef, ect. You'll need to learn to weigh your foods out so that you can keep on target. I would suggest eating 2 grams of protein per lb of bodyweight, per day. So if you weigh 150 lbs, thats 300g protein. You'll want to split that into meals eaten every 2-3 hours through the day. Add in a good carb to your meals and I bet that you make better gains than 6 lbs! heres a good cycle similar to what you've done, adding in a kick start, which will put a lot of water weight on you quickly, just starting your strength and gains. 

1-12

test cyp 500mg EW, split into 2 shots

adex .5mg 2x wk(more if needed on dbol)

1-6

dbol 30mg ED

wk 15 

pct starts 40mg nolvadex ED

wk 16-17

nolva 20mg ED