My brother is building a set neck 7 string guitar and he has a question about the truss rod situation. He's going with a bubinga neck with either a rosewood or ebony fingerboard, and the scale length for this guitar is going to be either 26 and 3/16" (I think) or 27". He's wondering what truss rod setup he should use. He's considering either a Warmoth double expanding truss rod, with or without steel rods, a Stewmac hotrod rod (I think that's also double expanding), or two truss rods. He thought bubinga was a stiffer neck wood, and to be honest I have no idea about that, or what truss rod option would be best in light of the stiffness uncertainty, so any help would be greatly appreciated. Thanks!