Most martial arts involve training for sudden bursts of explosive movement. As such standard traditional MA training isn't the best for cardiovascular fitness despite weight loss being a top reason why people sign up for MA in the first place.
You can repeatedly kick and punch over and over again to keep your heart rate up, but your form will inevitably degrade and I believe this is actually counterproductive to good martial arts training. I really believe you're trying to fit a square peg into a round hole. My suggestion is to follow a good modern training regimen involving jumping rope, calisthenics, and some weight lifting (it can be isometric if you like) if your top goal is to lose weight.
I haven't tried it yet, but that P-90X sounds pretty good. Says you can get ripped in 90 days? I guess it's possible, but......it's not a martial arts workout video persay. I guess there is that aspect of it, though. He does a kenpo cardio workout on his 3 dvd set. At least that is what the inofmercial says, LOL! Hope that helps.