Interesting, thanks for that RRD. Glad you're having progress with him.

As for the tofu...we're starting to eat it ourselves, and the ultimate goal is giving DS the same meals that we eat. We realize that's a way-down-the-road goal. Right now he sometimes gets deconstructed meals--when DH and I have tofu stir fry, DS gets red pepper strips, rice, a piece of broccoli, and we alternate between giving him a chicken hot dog or asking him to eat tofu.

DH and I are now talking about giving DS some time off from trying new things, based on a suggestion upthread. We're working out the terms before running it past DS's ASD therapists.

As for why the spectrum of foods we have him try is broad--we'd like to expose him to a decent range of things while he is still young. Some of them are practical--we want him to get to like cheese so he'll accept a cheese sandwich if he forgets his lunch and needs to take the school's default lunch. That sort of thing.
Another aspect of practicality--we have to limit what he's offered to try at his afternoon center by what's shelf-stable and nut-free.