Unfortunately, after having been ridden in that, it will likely take a pretty substantial amount of re-training if you wish to ride the horse in a snaffle. Even transitioning back down to a smooth curb will take some time and work. That's one reason why I thoroughly dislike bits like that. Because of the general mentality of people who use them (not you, OP, but the people who trained this horse before you got him), they are not soft with their hands anyway so harsh hands combined with a harsh bit is just a bad deal for the horse all the way around.
Since he is used to curb pressure, I would suggest a bit similar to any of these...
I've not tried either of these 2, but I really like the looks of them
This one has a bit of a flashier look with the decorated shanks http://www.kotrading.com/239091-part...turitybit.aspx
And I've got either a bit exactly like these or very similar and I've not found a horse that didn't like them and didn't go well in them.
The first few times you ride him in the new bit, you'll sure want to do it in an enclosed area like an arena or a roundpen. That way, he can't get completely away from you if something does happen.