Simply speculation on my part. But here's the deal. Kornerko will have two years remaining on a five year deal for ~12M/year. He's having a down year this year (buy low!), but over the last three years, his OPS has been 841, 932 and 929.
The tricky thing is to figure out if his slide this year is injury-related or if his skills are declining (he'll be 33 on opening day next year).
He provides the RH bat the Reds need without costing the Reds as much as a Holiday or Texiera would. His defense is probably not much worse than Votto's and it allows Votto to concentrate on becoming a league-average LF'er. His contract expires in two years, allowing time for Alonso or some other prospect to emerge. I don't know what the Sox may want in return, but I can't imagine it would break the Red's prospect bank.