Definitely use the SRM:RequestInterface_Create form. You need to make sure to include the 'z1D Action' = "CREATE" keyword/value in your request, which if everything goes well, will trigger the necessary back-end workflow to finish the creation of your request.
I am curious though, why are you trying to create the SRM directly. Normally the INC, WO or CHG creates the SRM for you. Or do you not have the ITSM module in your environment?
Did you ever get this to work?