Trade Turnbow for starting pitching if you can. Your offense is fine. See if you can get a Matt Cain type and maybe Fransisco Liriano or Ervin Santana to round out your pitching staff. I think it's unlikely you'll get an ace easily without trading your offensive studs, which you don't want. So, you will want a merely decent pitching staff with no glaring holes. This means no Maddux, D-Lowe, or Sosa. They will hurt you more than they will help. Maybe even take a risk on Daniel Cabrera cuz you need K's.
Please rate my team (posted not far below yours)