Thanks, everyone, for your input. I know Dr. Amend quite well (he tested both my kids) but we no longer live nearby . . . perhaps a phone conference is in order. And although I skimmed that book for other issues relating to my other child, I'll take another look at it with respect to sensory issues. Thanks for telling me what I already should have thought of!
It sounds like OT can probably help regardless of the cause of my son's sensitivity. Although I'm reluctant to have him tagged with a label, SID is a pretty benign one, and if OT will help, I'm all for it. He's already in a private school with a small class size (compared to public, not compared to his ideal!) so I think our ability to find a better environment is limited. The teacher is soft-spoken and willing to learn about sensory issues, which already is a huge thing.
Still open to more feedback . . . with gratitude.
