I think I have an idea.
While the instrument (SR830) does not have a specific driver for matlab, it does have a labview driver which seems to identify it as a VISA object (requiring NI-VISA), so perhaps if I can install that driver I can recognize it as a VISA object through either an NI or Agilent VISA interface. I will try installing the labview driver and NI-VISA, and then see if I can create the object via visa('ni', ...)
Any advice on making this work?