Hello,
I suspect there are typos in the file extensions you are reporting. You should be getting .1D.dset or .niml.dset from 3dVol2Surf. Of the two, I highly recommend you use the .niml.dset, which you get by using the option -out_niml in 3dVol2Surf. I also recommend you use the option -oob_value 0 .
The .niml.dset files can be read directly by 3dttest. There is no need for translation.
cheers,
Ziad