BabsR,
Having BTDT, I'd begin with an OT evaluation and a thorough assessment of his visual processing, phonological processing, and visual-motor co-ordination, if you haven't already. Addressing deficits that show up in any or all of these areas can, frequently, dramatically improve all of the skills that you mentioned. A good neuropsych eval is probably worth looking into as well, and could help you pinpoint what exactly is behind what you see, so you can implement targeted interventions.