SXTHXT_FSP fits combination SXT and HXT spectra, no spatial resolution! 
and
are uncompressed SXT images, 
and 
are uncompressed HXT data, from
an HDA file.
IDL> SXTHXT_FSP, index, data, hindex, hdata, fit_pars
SXTHXTBOX_FSP fits SXT-HXT spectra for a box chosen using LCUR_IMAGE. must be
the HXI structure, and are HXT images. You should be sure of alignment
beforehand.
IDL> SXTHXTBOX_FSP, index, data, hindex, hdata, fit_pars