Suggestions? Ok.
Practice makes perfect. If you're like a lot of people I've played with, you more than likely play on the line on defense to try to help with the pass rush, or maybe occasionally play the MLB spot in a zone....sometimes even drop a DE into zone. I would suggest taking control of your corners in practice situations.
rgw, you mentioned something along the lines of not being too good with that. Well, the only thing you can do is practice at it. I figured out really fast that playing the corners against WR's is a must if they've been passing well.
Second, watch it when they use motion before the snap. I've noticed the computer is pretty smart with that. They'll switch a TE over to make a safety cover him, then when the safety drops down I might get burned deep. That's where playing CB comes in handy. Also, watch when they use motion because sometimes you'll get a LB covering a WR. Must avoid that. I mean...this is all pretty basic crap.
The only thing I could suggest is recruiting players with high awareness. The play action kills me sometimes, and it's irritating. Doesn't matter, though, if you're playing the CB spot. I can't think of how many times I've said, "Where the hell was his coverage!?!?" and replayed it to notice that my guy bit BIG time on play action.
Something that I mentioned earlier was dropping a DE into zone coverage off the line. Helps tremendously when you're pretty sure they're not running. Usually the CPU doesn't pick up on that lineman playing zone, and it helps me.
Also, if they're passing well, and you're SURE they're passing, bring those damn LB's in. Bring in your quickest LB with the other LB's in a zone, and corners playing man with safeties in a deep zone, and 50 or 60 percent of the time you'll force a crappy throw that your guys can knock down or intercept. If you've recruited a decent D-Line, then this works even better. Bring a LB in from the right, pull your left DE into a zone(if you know they're passing). When the CPU sees the LB come in, he's gonna go to that open spot, but your DE will be over there to cover. You have the risk of getting outrun, but hell...it works for me a lot. I'm not talking about a defensive play designed to blitz LB's and pull DL either, cause I know they have those. Gotta be tricky your own kind of way.......Wow...that all seems kinda scatterbrained.
Pretty basic knowledge...and I don't know what else can be done with your defense on that game. Just gotta hope for the best. Don't give me crap about being down on Heisman mode and not being able to come back. I've done it three or four times against top 10 opponents. Granted, I've never been down more than 21 pts in a situation like that...you've just gotta be creative and pick the opposing defense apart. There's always weakness. I'm just not having that problem with the zone defense you're having, rgw. And the game's not crap, you're just obviously upset because you're having a lot of trouble with it. You get mad at the CPU DB's for missing passes, but will "be damned" if you're gonna try it and miss. Practice it and do it yourself. I have...I get burned sometimes...but I have. That little "swat ball" button works very well.
Just like on offense, when you're playing defense and the CPU snaps the ball, watch your defense form up and look for the holes. It ain't music theory, people.