Hi there - it SOUNDS like you're working your butt off!

I don't believe the "calories burned" things at all - you lose fat, or you don't. And the distance covered for HIIT doesn't matter either. It's the intensity.

You ARE doing interval training. I don't think it's HIIT, but you didn't say it was.

Now, my feeling is that MORE cardio is going to be too catabolic to muscle tissue. Every one is different in their tolerance to cardio. Mine is low- I tend to do well as a "weekend warrior" for cardio, and stick to lifting during the week. I will be adding some true HIIT back into my program sometime soon. Do a google search on HIIT or High Intensity Interval Training and see what you come up with.

One way to do it is to sprint/jog on a track or by blocks.

On a track, you could use a stopwatch with two timers, and try jogging for a minute and a half, and sprinting FLAT OUT for half a minute. Repeat 4 or 5 times.

On city blocks, you could try jogging two blocks, then sprint FLAT OUT for a block. Repeat this whole pattern 4 or 5 times (like sets). It's partly anaerobic, very hi-intensity, and BRUTALLY hard, but it's over with quick. I could not POSSIBLY do this for 20 minutes. I can barely manage 8.

Do it on non-lifting days, say, three times a week instead of your usual cardio.

I personally don't advocate MORE cardio for fat loss because it never helped ME as much as diet and lifting.

Diet and lifting should take care of body composition/fat loss. Cardio can be a nice extra hit, but for me, it's not the main story.