The main things to consider with Adeniums are:
1. These are tropical plants that thrive with consistent moisture in their planting mix
2. If the soil is dense and has a tendency to stay wet for a while after watering, rather than just moist, the roots will likely rot
3. If the soil gets too dry, the plant will likely lose it's leaves and go dormant
The use of non-compressible media is an interesting concept and worth experimenting with if one has extra plants, but if you have one or two prize Adeniums, I wouldn't risk it. Adeniums have been grown by thousands of people for many, many years in more typical media.
A good soil mix that drains freely is all that is really needed. Water well, let drain (don't let sit in a saucer of water), and don't re-water until the soil starts to dry. Adeniums don't wilt, they drop their leaves if they get too dry for too long, so that won't be a guide to help you learn Dig your finger into the soil. If it feels damp, it's OK. If it feels dry, then water it. This is especially important during winter when indoors. If the plant drops it leaves, keep the soil just dry-damp until it starts producing leaves again. When leaves start to grow once more, increase the watering. Try to keep the soil lightly moist and you won't have to worry.
As for summer rains, don't worry. As long as the soil drains freely and doesn't become water-logged, and does not sit in a puddle of water, you will be all right. This is the time of best growth for Adeniums, the time when they act like tropical plants that expect regular water.
