Good luck with your cleanse and getting rid of the impaction. I hope the magnesium works for you - I tried just p&b shakes in the beginning and ended up constipated, I then tried a mag cleaner with limited success and ended up doing the blessed herb cleanse which is mainly p & b shakes but with other herbs that help to loosen up old matter and followed up with a few colonics and I think that got most of the old stuff out.
I also used charcoal with P&B shakes recently to get rid of a tummy buy/diarheaa and it really worked. The charcoal makes the cleanse more effective as it absorbs the poisons/toxins and lessened the die off reactions, but I dont know if you can take it with a magnesium based bowel cleanser?