After July 29, SRM FITS files created by the RHESSI spectrum object contain the response matrix for every filter state that occurred during the time interval of the spectrum file.

In OSPEX, you set spex_drmfile to that one SRM file, and OSPEX will automatically retrieve the correct response matrix for each fit time interval.

SPEX can not read multiple SRMs from a single SRM files - it can read the file, but will only return the first SRM in the file.  You can use the hsi_break_srm routine to break the SRM file into separate files, each with a single SRM/attenuator state. 

Note: SRM = Spectral Response Matrix, also referred to as DRM (Detector Response Matrix)