I have found that taking 5-htp within too short a time after having come down from any MDxx often causes a greater stimulation, rather than the sleepy-time effect it has on me normally when taken before bed. Valerian root is actually moderately useful in the absence of benzos.
I would say that if one wants to sleep after an MDMA experience, or after using ANY stimulant, then regardless of your method of sedation, preloading with a healthy dose of soluble magnesium is the first step. Stimulants cause acute drops in Mg and regardless of how often you take them, you should be taking lots of Mg. Also, if you find that these effects are greater when you dose higher, consider trying to potentiate a lower dose, rather than trying to maintain the current dose.
Nootropics might help. Piracetam and a little choline make for a smooth transition from the speediest of peaks, into a relaxed place where one might sleep.
Try to increase absorption and reuptake and decrease the dose itself. I know that amphetamines/cathinones are absorbed best at a certain pH that tends to be more alkaline than the average coffeedrinking, sodachugging Human. You can potentially adjust the pH of your urinary tract over time, or shortly before ingesting your Moonrocks, and not piss out as much of the drug as you might usually. Grapefruit juice also is purported to inhibit digestive enzymes that metabolize ol' Molly, though this is speculative and you can find a ton of discussions over this around the forum.
Basically, try to get the digestion and usage of it in the body as efficient as possible, and you will suffer less negative effects. Theoretically.