It is possible to get from E to B with standard .105 strings. The important thing to consider is the gauge of the string core. Many 'light tension' strings use thinner core wire which require more travel to change pitch. We have determined that a core diameter of at least .022" is required for the Xtender to fully drop the tuning from E to B.
This is the case for all standard bass Xtenders as well as Xtenders equipped with the DoubleStop.