Make sure you start with quality soil. Some might argue that its not absolutely needed, but give your girls every chance you can to do well. I have no first hand experience with miracle grow, but from what I have read around here most people tend to not use it because it can be hot. No idea though, because another well known member here says it can be used easily.
Foil is a bad idea with stronger lights. Its not like mylar and other liners, it can actually fry your plants if its too close. I know you said you used it with good results before, but your new lights are a lot stronger. Just be careful, would hate to see hard work go down the drain because of foil!
Aside from that though, I have no idea what the issue could be. If you have any seeds left id suggest getting some Fox Farms Ocean Forest (or happy frog if you're afraid of burning, but I havent had any issues), fill a solo cup up with it, and plant your seed. If it comes up good and grows fast, you can assume it was your soil. Then put that seedling in your new grow area. If it does well, it was only the soil you were having problems with. If it starts to die then you have other issues you will need to work on. Could be heat, stale air, reflection from the foil, whatever.
Hope this helps!