To open up space for Cody Ross (The Reds are 1-0 in games he has played) and to bring back Tony Womack. Womack was granted his unconditional release on May 3. The Reds were 19-8 at the time but they have only gone 4-8 since. His lack of veteran spark must be the cause of the offense's slump. May 3 was also the day Ross went on the DL.
Dunn and Griffey can then be moved to the Yankees so they can platoon in left field (Reenactment Jr to play against lefties) and the Yankees can send a bunch of pitching prospects from the low minors because the offensive slump is caused by the Reds bad bullpen and lack of starting pitchers.