You could also look into power lifting. I spend the last two and a half year and never really put on any huge muscle only in the past 6 months have i started going for failing at 6-8 reps and I have put on more muscle then I have in the past few years.

Crossfit would probably be better for training the endurance of your muscles and such.

Also as long as you do your stretches and keep up with your flexibility stuff you should still be able to maintain it even if you get big.

Micheal, I am 5'9" as well and I weigh in just under 160ish, I am lucky I did not listen to the guys in the gym or I probably would be where you are, a lot of them always told me to put on 40 pounds and then you can start lifting big, I was always told that mass lifted mass which is why I started training the way I am, just want to make sure I keep it lean.