You might try riding English with a curb, and western with a snaffle. There is no requirement to ride English with the horse 'on the bit'....He was very soft on a curb bit with shank. He hates the snaffle and I can tell that he is tuning me out and messing with trying to expel the bit...
When I swap out my Australian saddle for my English one, Mia looks like this:
I've spent the last few rides trying to get her used to a new bit. In theory, it should be gentler, with more even pressure on the tongue and less likely to 'bite' on the bars...but I'm not sure she is convinced. I raised it up a hole yesterday while loosening the curb strap a hole, and she seemed content the rest of the ride - although a curb bit placed with a wrinkle in her mouth seems a bit odd to me.
She learns new things best if I break everything down into the smallest steps I can. Even a simple bit swap can have her thinking and fussing for a few rides. Sam might find it easier to learn if he takes smaller steps.