Hearbuilder has online demos available, so that may give you some feel for the program. I remember doing the demos way back when the program first came out, but we ended up not buying it. We did Earobics (both stages) and I think that benefited DS a lot. I was able to get Earobics for free from on of the local special needs resource libraries. You may want to check if any such libraries in your area have Hearbuilder.
I agree with sste that visual processing disorders can take on many forms and you will need to know the specifics of his challenges to develop a plan. Some doctors believe Irlen syndrome is caused by other eye issues. Has he been seen by a pediatric ophthalmologist to rule out any structural issues? DS has complicated vision issues and gets a Functional Vision Assessment done by the special ed regional center. But he has a low vision/ vision impairment diagnosis. I don't know if they do a FVA for processing issues.
Gena
DS, age 11 and always amazing
“Autistics are the ultimate square pegs, and the problem with pounding a square peg into a round hole is not that the hammering is hard work. It's that you're destroying the peg." - Paul Collins, Not Even Wrong