HIIT vs. Fat Burning Zone...need guru's

Ok, I am planning on seeing a specialist who works with athletes. She has an extensive RMR test and V02 & VC02 Max tests and she's not in a gym. This is all she does.

Anyway, I had a chance to talk on the phone and ask a few questions but I still find myself confused.

I do P90X and Insanity hybrid 32F 5'9" 178lbs 28%bf, 128.5lbm

1lb of fat loss is 3500 right?

So I start getting confused when we talk about different zones using a higher fat ratio vs. a higher carb ratio. If I burn more calories faster wouldnt that be better? She talked about resting is actually when majority of the progress is done. And alot of people who do HIIT actually end up Anaerobic at rest. If I can incorperate some fat burning zone (whatever mine is) that will teach my body to be more Aerobic at rest. She's not saying to drop weights or HIIT....but to incorperate the zone into my training to create a more well rounded approach.

So when doing HIIT and Im burning more carbs that fat....what does the body burn after my carb stores are gone? I do find that I get low sugar from doing work outs even when properly fueled. Her goal is to keep lean body mass, and when athleates perform their bodies draw from mainly fat stores (in say a marathon) which helps them with longevity, ect.

So if someone could explain how losing 1lb of fat aerobically vs. 1lb of fat Anaerobically...that would be helpful....and any other insight. I have several years of very hard training under my belt, but have always felt like my efforts outweigh my progress.

Thanks in advance