I emailed DPA asking about the D:Vice MMA-A and USB_C. Here's what they said.
"If the customer prefers not to change the setup, I would strongly recommend sticking with the current version of iPhone. While we haven't had the opportunity to test the new iPhone 15 yet, we anticipate that with the microUSB-to-USBC cord, the MMA-A will operate as a sound card for the iPhone - just as it does when used with computers and iPads. However, please note that the app for the iPhone may have limited or no functionality.
Please be aware that the MMA-A was discontinued in June 2023. As a result, DPA will not be releasing any further updates for the device or the app."
So does that mean you just won't be able to adjust gain?
I don't remember the DPA app actually doing much.
Then I asked Shure about USB-C cable options for the Motiv accessories, since someone here recommended their cable as a more rugged cable than the one that comes with the MMA-A. They said:
"Thanks for contacting Shure. We offer our AMV-USBC already! It is readily available for purchase here:
https://www.shure.com/en-US/products/accessories/amv-usbc15?variant=AMV-USBC15So, what happens if you use that cable with an iPhone 15 and the MMA-A? Will the DPA app refuse to work with the MMA-A because it doesn't detect a lightning port?