Hard to tell what's going on here. The media doesn't seem to know, except for the initial players announced. A lot of people think Garrett Jones is involved in the deal. Maybe Iglesias, whom the Pirates seem to like. The Sox need a first baseman. Jones hits only RHP well, so they would have to have Napoli or somebody else to hit LHP. The Pirates also have another big power guy, Robinson, a LHH, and Gaby Sanchez, a RHH, to play 1B. Jones is also listed as a right fielder on the roster, which also fits in with their needs. Jones looks expendable, with a salary of $2.2mil 2012. Maybe more in 2013.
Could be they are trying to balance things out in a deal which keeps them under the luxury cap. Could be they are juggling Napoli right now, and that could be a factor--in the cap and the 1B situation. Could also be there is banter about Iglesias or Kalish--or whoever the Pirates want for Jones.
The elements of the Pirate deal could hinge on what they do with Napoli. If they get Jones, I suppose they have a fallback of Gomez at 1B against LHP. Gomes isn't bad at 1b--made one error in 13 starts for the Sox there last year. .987 fielding % in the minors. Much worse at 3B.