@IanCundall
With the reported additions of Downs, Mata, Houck, Duran and Groome the Red Sox player pool will be at 55. Save for Groome, who is a unique case, all of the prospects who are going to be added played in the high minors last year. Most notable omission, thus far, is Triston Casas.
Groome is being added because he must be put on the 40 man roster at the end of the season if they want to keep him. Due to his injury issues, he really needs to get reps so that the Sox can figure out if he's worth the 40 man spot next season.