Unless you address the problem at it's root cause, then there is no chance of improving his condition. Call me radical, but the cause of such 'distortions of sensory processing' are in the brain and so it is the brain which must be influenced.
There is a great deal of neuropsychological evidence that the cause of these problems lies with two structures in the brain, one which controls our 'sensory attention,' (the reticular activating system) and the other which acts as a 'switchboard,' directing incoming sensory information to the cortex for further processing and analysis. (This is the thalamus).
When these two structures are miss-tuned, several things can happen to the child's ability to perceive the world around him. He may become hyper-sensitive in one or more sensory modalities; - he may become hypo-sensitive, he may only be able to pay selective attention, sometimes seeming obsessed with specific sights, sounds, sensations; - he may have trouble screening out extraneous sights, sounds or sensations, experiencing all incoming sensory information simultaneously; - his sensory attention may be tuned inwardly and he may experience sensory distortions produced by his own system, much as a migraine sufferer experiences a visual display.
Obviously we behave in the world according to what we perceive and so each of these sensory distortions produces distorted behaviour.
The good news is that these two neural structures can be retrained, - retuned! This happens in healthy, uninjured people all the time as a matter of course, as our brain constantly re-adjusts it's functioning to the environment in which we find ourselves. Of course in our children who have neuro-developmental problems it takes a little more stimulation to retrain them, but it can be done by the construction of an adapted sensory environment.
If you want to read more about this then there is a book called, 'Brain Injured Children: - Tapping the Potential Within.' It can be purchased here. www.lulu.com/product/paperback/brain-injured-children---tapping-the-potential-within/10642919
It is also available through the Snowdrop website at www.snowdropcerebralpalsyandautism.com