I am still working on this and was wondering if anyone had any suggestions, since I feel like I'm missing something quite obvious.
Is the appropriate approach to convert the 3dttest++ output (i.e. twominuszero_lh.niml.dset) to a volumetric dataset using 3dSurf2Vol? I was under the impression that one of the purposes of doing the surface-based analysis directly through afni_proc.py was so that the surface results would be directly mappable to the volume, but I may have misinterpreted that.
Any ideas would be appreciated!