i'm still a beginner in sprinting, but looking at your bounding video, I can give some suggestions, which i hope you may find helpful.
I remember there was this website, which taught bounding, but can't remember the link, but they provided a step by step progression approach, which was skipping, skipping for height and then from there to bounding as bounding is like skipping for height.
secondly, the second video is better than the first video, but the description you gave about your heel hitting the ground first rather than forefoot (balls of your foot) looking at your video, is a result from when you are bounding, you seem to drive the feet down hard and emphasize on bringing knee's; the quick high knee to quick driving your feet down is slowing you down and making you less elastic, so something you can try, is from running start, when you bound on the first step skip high and your knees should go up, don't bring it any higher, than instead of driving down hard, think of letting your feet ahead but without emphasizing on reaching too far ahead, just extend your legs when in the air and coming close to the ground you should land on your fore foot and think of pushing of the forefoot and repeat with the other leg.
That's the only thing i could spot from the video, just my 2 cents.
some videos on bounding, you can see he doesn't bring knees high but parallel and the feet doesn't drive down but the lower leg extends before driving down. but don't recommend on concrete, which they were doing on in the last part of the video.
http://www.youtube.com/watch?v=zSYq1GrCjlI pc