For what it's worth ...
After YEARS of me (starting as a young grade school age child, until about 18years old) getting into heated discussions about my hearing and what I could or couldn't hear, verses could or couldn't UNDERSTAND with my various audies.
Basically, my audiograms have always indicated that I should be able to understand and react to sounds/speech at one level, but my "real life reactions" (including listening comfort levels, understanding speech etc) indicated that I either somehow had more hearing loss than my audiogram showed, or there was something else going on...what that was - they didn't initially know.
Eventually my Audies concluded that in addition to HL (profound +120db right, mild/mod flux left) I also must have APD (at least a mild form).
The problem is that, as others have mentioned CAPD/APD is effectively un-testable in those with hearing loss ... instead it's diagnosed by observation and once the person is old enough by the individual explaining what the world sounds like to them.
It wasn't until I actually got my first HA at 25ish years old (for the mild/mod side) that they were really 100% sure that I must have APD - in order for me to UNDERSTAND I have to be over-amplified.
Even though I can detect pure-tones (ie my AGram levels) at lower levels, in order to understand what is being said I need things about 10-15db minimum more amplified than my AGram indicates I "should".
In addition to this - while all Hoh/d/Deaf struggle to understand speech/sounds when there is background noise ... most of the time, I end up what I call "functionally deaf" in anything other than minimal background noise - especially if the voice I'm trying to un-scramble isn't one that I'm intimately familiar with (mu, dad, sister, etc).
I also have in interesting thing happen some times if there's a lot of noise, if I'm tired (especially when falling asleep) etc ... when listening to things, if my brain gets too overwhelmed instead of "focusing" on the sounds, it's almost like my brain locks the sounds out - I either only hear a "shhhhhh" like white noise, or it's like a loose connection - everything goes silent (the silent "loose connection" thing happens ALL the time when I'm starting to drift off to sleep).
In my case (and many others with APD/CAPD who I know) we are very visual learners - making learning and using ASL etc in ADDITION to English a HUGE advantage.
Although I was raised without the benefit of ASL as soon as I started learning it - I realized that it made FAR more sense to me - my brain naturally "got it" was able to understand it and learn THROUGH it in a way that I'd never been able to with English (or other spoken language). In fact once I was able to hold even a basic ASL conversation with my ASL teacher I started asking for help sorting out some of my English mis-understandings including how to properly use "than" verses" then etc ... things that my English teachers had tried to explain over and over again - but for some reason it wasn't until I SAW it in ASL that the rules of use made sense.
Learning ASL was a KEY to be being able to completely understand a number of factors regarding English (which I'm sure sounds odd ... but it's true!).
While I fully understand that you want Tyler to be able to function both orally and using sign ... my personal suggestion (as someone with HL & APD) would be for the moment surrounding him with as much visual language as possible, ie ASL (or SEE I/II if that's your choice) and then once he's got a good gripe on how language works expressively and receptively (ie is using ASL to express his needs, wants and understands what is being signed to him) then I would add back the English focus. continue to voice as much as you want just make sure that he's surrounded in signs for everything... you may be surprised at how quickly he jumps forward in language!
The reason for my suggestion is that he's at a critical age when that language centre in his brain is forming - when he's acquiring a "language base/foundation" that will allow all future language to make sense ... if he's struggling with English/spoken language but is absorbing Sign...then for the moment Sign (ASL) will be the most reliable way to ensure he has a solid language base forming. Once he's thriving using Signs and understands the POWER of language ... then English will "make sense" in a way that it may not right now for him. Once he understands that forming signs together creates the ability to communicate ideas - then the same "connection" can be made with English and communication
Of course as Tyler's parent - communication options are YOUR choice ... my intent isn't to do anything other than explain "from the inside out" (ie from someone with hearing loss & ASD) what my experiences have been & how acquiring language made "sense" for me.
The scary thing is that while there are a number of really GOOD "professionals" out there ... there are also a lot of BAD ones! My parents where given information that effectively bullied them into a single communication strategy (oral only) even though I ASKED to learn sign as well - however the "professionals" scared my parents (and many others) into believing that if children with HL learned sign we'd all stop talking ... which of course is completely untrue (in fact in many cases including my own ASL helped with English understanding, comprehension, grammar etc)
There's no way to reliably test for APD/CAPD especially in those with hearing loss ... however if you are able to track down a GOOD paediatric audiologist who specializes in speech and processing issues they may be able to help.
