Noise-cancelling headphones and an MP3 player-- I use that technique to "filter" unpleasant auditory sensory input, to which I am also very sensitive.
A reed-diffuser in his room might help mask smells that he finds distressing.
Does your DS find guided-imagery relaxation/meditative methods effective? What about when used in conjunction with a comfort-texture/smell?
I might try that route. It's also a known method for managing pain, so it could be used as a means of managing multiple challenges simultaneously.
