DB's DL's (or BB) can be considered a like version of a squat, but not giving the same effect. In any DL, the upper body and arms are holding the weight stable as the legs do the actual lifting. The difference being, that the weigh lifted in the DL is below the hip/back area. While in the squat, the weight used is well above the hip/back center of that important core, or pivot, point. Each will have a different dynamic on the legs and upper body. Lots of old exercise theory's about that center of power (hips/back and the ab wall) in heavy lifting. More power (and muscular development) seems to be generated with a weight being held below that center body area, for most people.. Hip lifts for example, where huge weights (usually with a enforced lifting belt and chain) can be hoisted in regular workouts. And most are done in the higher rep range.
DB's can work well when doing DL's. The point being that the thumbs are facing forward in a more natural position. And more important, the knees are clearly out of the way of the lift. If you do not want to start the lift that low, with a pair of DB's, than place them on a set of heavy boxes/benchs, etc and stand in between. If you want to go lower when doing SLDL's, than stand on a box.
A trap/shrug bar would probably work best of all. Because,with DB's, they tend to rub against the thighs when a heavy weight is used. With the trap/shrug bar, this can not occur. In any event, DB or trap/shrug bar,the weight lifted is more along side and inline with the natural lifting force of the body when coming to a standing position. That a equate to less injury potential in the long run. Good Luck.
