Tony,
I'm confused about your question. First, you ran a two- (not one-) sample t-test. And you do have two sub-bricks in the output as shown below in the output of command "3dinfo -verb ZZtest.nii":
Number of values stored at each pixel = 2
-- At sub-brick #0 'SetA-SetB_mean' datum type is float: -0.892368 to 2.86044
-- At sub-brick #1 'SetA-SetB_Tstat' datum type is float: -2.73431 to 10.4144
Gang