The digestive enzymes are good, but probably will not effect your constipation.
I'm glad to hear that you are passing gas...that means there is not a complete obstruction. However, stay away from any foods that you know produce gas while doing the colonics because the gas may prevent you from releasing more.
I would suggest that while you are having the colonics you keep your diet extremely 'clean' and avoid any flour products incl. breads, pastas and cereals. These tend to gunk up the pipes (flour+water=paste!) and could make it even more difficult for you to release. Eat LOTS of fresh vegetables and fruits. juicing is also very good.
Since you can take milk of magnesia...obviously you are able to take magnesium, just not in the sulfate form (ES). There is a product called Natural Calm, which is powdered magnesium citrate...and I recommend it highly. It can be used in lower doses for a great magnesium supplement...or higher doses to clear you out. It comes in several natural flavors (Raspberry-Lemon is my fav) and it is sweetened with stevia. I would recommend that you get some of this and take a Tablespoon before bed. This should get things moving and also give you the magnesium that virtually all of us are deficient in. You may need to adjust the dosage up or down to get these results. If you are extremely deficient in magnesium this may not be enough to loosen you up.
I would also massage your ileo-cecal valve every day...and more often won't hurt. This valve (that separates the small and large intestines (colon) is located about midway between your belly button and your right hip bone. You may have to really dig a little, and you will know when you have found it because you will feel a little gurgle or clicking sensation. This valve can get stuck and may also contributing to your lack of releasing.
I hope all this is helping! Don't worry...we'll get you going!!!