RNB - I've heard about P90X, all I know about it is that it's some regime a lot of people in the US seem to use to get toned quicker.
Some people don't want to just look plenty toned. Some want to be able to build muscle mass, proper stamina, concentrate on specific muscles, speed up the process and so on for quite a few reasons (punching heads off shit being one of them). And there are much more efficient and better ways than to do it with just push-ups, sit ups and cardio. I'm not saying they don't work, because to a certain degree and with a correct diet they'll get results, but there are much more efficient methods if you're willing to put the effort in.
As for burning more fat, do something like HIIT and the running part of it doesn't need to be more than a fast jog. When you're just constantly sprinting you start burning away at the muscle too and sometimes completely bypass the fat. Maybe I'm being picky on what constitutes running and fast jogging and shit, so let's just taking jogging out of it and leave it to walking, running and sprinting. For HIIT, if you're using a treadmill do about 2 minutes walking at around 5-6kmph then run for a 1 minute at around 10-11kmph, then back down for 2 minutes. That alone for about 15-20 minutes will burn a lot of fat but also keep burning fat for quite a while after.
Weight training itself will also burn a lot of fat too, especially if you're doing lower weights at higher reps, and doing cardio after a weight workout will burn more fat and build more muscle as opposed to if you did your cardio routine before it.
A method of getting strong endurance is called Fartlek, similar to HIIT but it doesn't have as set of a structure. You basically walk at a decent speed until your body warms up, can be about 5 or 10 minutes, then run or sprint till you're out of breath, then back down to walking to cool down for another 5 or so minutes till you can run again. Repeat that for about 45 minutes, someone I know did this for 5 weeks straight and was about to run a complete marathon after it.