I believe that the information you are looking for is contained in section 12 (GPIB Programming)
of the DAS 9100 Series Operator's Manual. A PDF is available in bitsavers.org's Test Equipment Archive,
as well as our TekWiki (w140.com).
In particular, I think you will be interested in the ACQMEM command to transfer the acquisition
memory to your computer, as well as the MNEMONICS command to transfer the Define Mnemonics
menu setup to and from the DAS mainframe.
As far as I know, DAS 9100 uses the RS-232 port as a poor man's GPIB interface, so these commands
should work over RS-232 as well, though I have not tested this myself.
According to the Tektronix 1985 catalog, Tek used to offer a suite of UNIX software tools (91DVV),
with source code (!), for generating test patterns and transferring data to and from the DAS.
Incidentally, I still have a working VAX system, so if someone has these old tapes gathering dust,
I would love to get a chance to preserve and archive them.