I just noticed that the Zone Diet category on this forum is gone.
The Zone Diet is too low in protein to get that lean while maintaining muscle mass, unless you're naturally lean. You should be eating anywhere from 1-2 g of protein per lb of LBM.
Getting to 5% bodyfat is extremely difficult for most, and you might not be able to do it on a simple Zone-type diet.
I'm also going to guess that you're underestimating your current bodyfat % and that you don't really know what 5% body fat looks like. 8% bodyfat is RIPPED, if you have some muscle. 5% body fat, as Derek said, is bodybuilder status. Even bodybuilders rarely maintain 5% body fat. Martin Berkhan is the only person I've actually heard of who maintains 5.5% body fat year around and is not an endurance athlete.
If you're going to try to maintain anywhere close to 5% body fat year around, you're going to have to implement frequent refeeds and some other nutritional strategies far more advanced than the Zone Diet.