Good news. I did hear back from Dr. Choureri. And, as I suspected, it is indeed possible to dispense with the purchase of the Babyface if you have another interface such as an M4. This will lower the price of the Audiophile package by $700. Also possible to pay only the price increment to upgrade the package from one tier to another.
So it would be possible, for example, to buy the introductory software for $980, and, if you like it, pay another $3300 at a time of your choosing to upgrade to the Audiophile package--provided you already have your own interface.
Obviously, this makes it a more sensible, if still expensive purchase. If it doesn't work for you, you would find out on the introductory version and only be out $980, an expensive but manageable downside. The upside could be something amazing. Maybe.
A possible project for next year after I get a Mac Mini M1.