As an OT, these are interventions that I have seen work wonders for children with dyspraxia:
*Therapeutic Listening
*Interactive Metronome
*SI based treatment with LOTS of gross motor movement through space
*Perceptual activities that involve gross and fine motor coordination, laterality and directionality, language, vision and auditory processing
* Play that involves sequencing, timing, planning and executing movement
For hypotonia:
* play activities that activate the core muscles and work the child to fatigue
* SI based treatment that activates both the vestibular and proprioceptive systems
* Nutritional support, including pre-digested protein drinks (like the body builders drink) or supplements such as Carnitine, Coenzyme Q-10, B and E vitamins and alpha lipoic acid.
I'm much bigger on the "bottom up" approach to OT with these issues, but it seems like your son needs a "top down" approach in conjunction with it! Have you seen the Dyspraxia Foundation website?
http://www.dyspraxiafoundation.org.uk/Lots of great info here! Maybe he'd like to read some of it.
Best of luck. I'm glad you know what you are dealing with and that now you can continue to progress forward!