I do believe that Fitz is trying to keep these documents secret because he lied to the courts about the reasons for necessity of their testimonies, and misinforming and misleading the court about the "classification" of one Valerie Plame, sine qua non of his "investigation".
I have no proablem with reporters having to testify. But I find it interesting that Congress wants to protect reporters while not giving the President the same protection. They want everyone he talks to be under oath.
If he didn't lie to the courts, they'd be the only people Fitz didn't lie to regarding this case.