[Freesurfer] mri_matrix_multiply to move functional images to common space

Hi,

I'm trying to move a bunch of partial FOV functional images (occipital cortex only with oblique coronal slices) into common space. For each subject, I have a registration file (register.dat) to register functional images to anatomicals, and I'd like to incorporate the talairach.xfm registration so that I have a matrix that registers the functional images to the mni305 volume. I've been using the following, but registrations aren't coming out properly:

mri_matrix_multiply -im register.dat -iim <subject>/mri/transforms/talairach.xfm -om reg_to_common.dat

I'm checking them using tkregister2, but the results don't look great. Is there a better/easier way to do this? Thanks!

Andrew