Ah the P90X is just for fitness really. If you're trying to build muscle continue your weight lifting as usual. I only use the P90X to keep in shape, its not as intense as my MMA, and conditioning training. Just enough to keep me in shape, but I do notice the difference it makes on my MMA training it makes me feel stronger.
The P90X does muscle confusion, so they don't get used to the same workouts. When the muscles get used to the same workouts you don't gain anything when you workout. With all the muscle confusion you'd be doing, you'll definitely notice a difference in your weight lifting if you're trying to gain muscle.