I haven't seen it too much yet and haven't gotten good at reading it yet, so I honestly can't tell you.
There's only a slight difference between Cover 3 and Cover 6 however. Cover 6 just allows more space on one side of the field and less on the other. And the only time it's really important to read Cover 6 is when you're sending 4 receivers on fly routes.
In this case, if the two deep covers are on the left and one is on the right, you might pump fake toward the farthest right WR to see if the safety on that side bites to him, and then quickly launch it to the closer guy on the right side (meanwhile ignoring the left side, because whichever guy you throw to will have at least 2 or 3 defenders on him by the time the ball gets there).
Ultimately though, when you see Cover 3, Cover 4, or Cover 6, you should be throwing to your release valve guy or running for it yourself with your quarterback.
As for those who post in this thread and still complain that the passing game is too hard, I have to ask, did you even read any of the posts in here? Or are you just adding a complaint that you think it's too hard, and you're not willing to put in the effort to make yourself a better passer?
And for those of you who have read the posts and are still struggling, what is it, specifically that you're having the most difficulty with? Perhaps you can upload some replays of your bad pass plays and we can analyze them? Either way, if you can describe the trouble you're having, and what difficulty level you're playing on, that'd be helpful.
And personally, the offense I play is a ground-heavy pro-style offense. I rarely have more than two receivers on the field, as I'm usually in an I-Form with a tight end on the field. I'm using short and medium passing game with big possession type receivers in order to keep the defense honest on my ground game.
But it's not necessary to run the ball very often at all in order to maintain a successful passing game. When you're passing the ball more often, you do need two things though.
1) A good quarterback. The coverage will tend to be significantly better, and you'll rarely find the WIDE open guy in a pass-heavy offense. Your quarterback needs more arm strength, accuracy, and yes, awareness. Even human controlled quarterbacks need awareness. Better awareness impacts his ability to put the ball in a place for his receiver away from the defense.
2) A good familiarity with a LOT of pass plays. In a ground heavy offense where you run the ball 30 times and pass the ball 15 times, you can get away with only knowing about 5 different pass plays. And it can be something like 1 short pass play, 1 medium pass play, and 3 play action pass plays, and you'll be fine. Defense will be too worried about your run game that they won't often be able to pick your passing play call.
However, when you're air-heavy passing like 35 and running 10, you have to know a lot more passing plays. You need to be comfortable with 20 or more. And it needs to be a good variety, a good mix of plays. And you have to be confident in your QBs ability to scramble for at least 3-5 yards if need be.