Diet is really the key. If there is caloric excess - you will gain weight. A good program will ensure that most of it is muscle. If absolute weight doesn't change, you might get some body composition change (i.e. the calories that were previously directed to maintaining fat stores get redirected to newly built muscle). This is a lot easier to pull off if your body fat is relatively high - once your bodyfat is decently low the body is very resistant to trading fat for muscle as the body's primary purpose is to survive (hence you wind up with bulking and cutting programs). Also, as you continue to add muscle your base caloric requirement increases (even if weight stays the same or decreases, it takes more calories to maintain a pound of muscle than a pound of fat. So you wind up with a scaling need for more calories as you increase your muscle mass and weight.
Anyway, at 12% - I wouldn't try to pull over the body composition change. You might get a small margin of success but it will be short lived. You'll sacrifice a lot of potential muscle. If you were at the 20%+ point, this isn't so hard.
So anyway, you need a good program - the periodized version of the Starr 5x5 is pretty popular here but if you don't have a number of years of hard training under the bar you'll make equal and possibly better gains with the single factor novice version (periodization is a curse, not a blessing - if you can make good gains without it, hammer it for all you can).
Hopefully you are familiar with the lifts. There are descriptions of the powerlifts here (very good ones - read them no matter how proficient you think you are in training):
http://www.midwestbarbell.com/totalelite/index.php?showtopic=14. My main thread is here:
http://www.elitefitness.com/forum/showthread.php?t=375215. You'll find the programs (The single factor and dual factor/periodized), the correct way to do rows links, and some links to sites with videos of exercises.
So between a good program (and the Starr 5x5 has obviously proven very successful here recently and elsewhere over many years - at least as good as anything out there when applied to a broad range of lifters and athletes) and adequate food intake that should take care of itself. The program will get you very strong very quickly in a very viable hypertrophy volume range - this is all a program can do (and even the people that didn't eat to gain muscle or were cutting can vouch that they got much stronger so obviously the mechanism is in place), after that it's diet and your body. At 6'1" and 176lbs, you have a lot of potential growth in you but some will gain quickly while others will gain slowly, that's just the nature of the beast. This is a more in depth post on diet and caloric excess which you should read carefully:
http://www.elitefitness.com/forum/showpost.php?p=4866519&postcount=465