I've read some of your earlier posts, and I may be wrong in this assessment, but seems that your assumption has been that your son has extreme hearing loss-- which would have potentially explained his speech issues.
So I can understand why it would be confusing to hear from the doctor that there is minimal hearing loss-- as this might raise more questions for you than it answers.
I think you should proceed forward with the tests he suggests, and perhaps see another doctor for a second opinion. But if you haven't already, I would definitely get a full developmental assessment to fully understand what issues might be contributing to the speech delays -- and also explore if there are possible sensory integration issues (as a previous poster suggested in relation to the fear of water/baths that your child was experiencing).
All the best with this -- its so hard when we are trying to help our children and we don't fully understand how we can best serve them. You sound like a caring mom and I'm sure you will find your way through this. Be patient and don't let your anxiety overwhelm you in this -- just methodically continue pursuing the help your son needs. Good luck