depending on which soft maple you are talking about red leaf is harder than silver maple. both are more plyable than hard maple however I don't think the kind of bend you are talking about would be a big deal for any.. I could be wrong.
Most of the veneering I've done has been with commercial solid products. Their thickness is around 1/40" and will make a pretty tight radius. When making my own veneer, I'll resaw and drum sand to less than 1/8" down to less than 1/16", depending on the project. I've used a lot of bending ply, but have also used poplar for the filler if I'm not making a really tight radius. I'm thinking a 6' radius could be done with any type of wood, if you process it to 1/8" thick or less.
Yeah, that could be a problem. My Performax will handle the 3/32", but 1/16" can be a problem. Fortunately, if I surface one side of the thick stock I can resaw on the Laguna (with Resaw King blade) and get a pretty much ready-to-use piece. I love that blade!