Agreed. Ellsbury's their best chip for a big bat, and the Sox don't have a pressing need for the Reds' best chip -- pitching. If the Reds are going to make a significant deal, say for a player like Reyes or Ellsbury, it's going to have to involve pitching. There's no top-shelf major-league ready prospect who could land a top player. (Alonso, Frazier, et al, are not elite prospects at this point.)
Sox are a tough match-up for the Reds. Maybe Alonso would interest them some and if the Reds could add some other pieces from lower in the system, they could use them to piece together a package for Adrian Gonzalez. Something like Alonso, Heisey and Boxberger might work, but if the goal is to put together a package for Gonzalez, the Pads would probably rather have Ellsbury.