RE: Cardio and the
As Sarah says, P90X is set up to minimize cardio to reduce any cannibalization of muscle tissue (though it's actually probably more like the cardio burning up the fuel that would otherwise go to feed growing muscle, because to grow muscle, you have to increase calorie intake. If you did no weight work, then the actual 'cannibalization" of muscle would take place).
There's probably no 'secret formula' that works for everyone, but I think if you want to focus on muscle building, you have to decrease cardio somewhat (moderate cardio, or short bouts of cardio). If you want to lose weight, then more cardio, including intervals once or twice a week, along with probably whole body weight workouts or circuit cardio/weight workouts.
It seems difficult to both lose fat and gain muscle at the same time, since the former requires a calorie deficit, while the latter requires an increase in calories. That's why bodybuilders focus on one thing at a time, and usually get both big muscles, and some extra fat, during the bulking stages, and burn off the extra fat while trying to maintain muscle in the 'getting ripped" stages.
I think that doing both at the same time is possible, but more likely to give only moderate gains in both.
As for functional fitness, it doesn't seem like you're using the term as it is usually used : movements that mimic those used in daily life, with an emphasis on moves in all 3 planes of movement (saggital, or forward and back; frontal, or side-to-side; transverse, or rotational), compound movements, moves using balance, large range of motion, etc.
Why not focus on gaining some muscle now (in the winter!), and focus more on gettig rid of the extra fat closer to summer?
P90X is a great program for gaining muscle and avoiding excessive cardio (either too long or too intense) that could slow those efforts.