Robert,
I attempted the switch you mentioned. /a generates an error from windows installer stating "invalid command". I think I have found the base Visio installer .msi. Is there a way to chain multiple .msi's in a package/setup.ini or in a transform for the base .msi? I've tried this before with this same product without success. I have the same issue with SAP 6.2C2.
Thanks for your time,
Bryan