My DD was diagnosed with dyslexia at age 8 earlier this year. We are also doing Barton Reading and Spelling. For Math, we switched to MUS recently and she is excited about it for a change. She tends to pick up the concepts quickly when she can see visually how they work (we started out in RightStart and it was a good fit for a while). She takes a while to become solid on math facts though so I am debating adding in CLE math due to the type of built-in practice and review.
I have read of some dyslexics liking Teaching Textbooks, but when I showed the samples to my DD she hated it. The biggest thing for her is to be able to see concepts demonstrated with hands-on items and then clean math pages. She does like to visualize in her head the math once she has seen it demonstrated. Some dyslexics have done well with Singapore Math (not my DD) and some CLE math as well. Ronit Bird has a lot of great information and teaching strategies for dyscalcula (like dyslexia for math). Her ebooks are pretty inexpensive and I'm about to get her dots book for my kindergartner and the times tables one for my 9 year old.
If your son struggles with subitizing I would go straight to Ronit Bird. He may also be struggling with it and not realize it as well. http://www.ronitbird.com/ Many kids often move onto other curriculum after Ronit Bird's materials, but I've been told the foundation is amazing for those who otherwise struggle with math.
I highly recommend the Dyslexic Advantage by the Eides. It really helped me understand and identify the strengths my DD has better which has helped in other areas and even in curriculum we choose. Overcoming Dyslexia by Sally Shaywitz is a good book too. I have on my list to read The Dyslexia Emplowerment Plan as well, but haven't gotten to it yet. Homeschooling Your Struggling Learner by Kathy Kuhl is also good and has helpful tips.