@bigfishcatcher I believe the USB A is only, at this time for a connection to a USB-A to RJ45 network cable adaptor.
From the manual
USB A: Connect a USB Ethernet-to-USB A adapter (sold separately) to connect to a network for internet access (as an alternative to using Stadium’s built-in Wi-Fi)—see Wi-Fi, Ethernet, and Bluetooth Connectivity.
USB-C®: Connect to a macOS or Windows computer to use Helix Stadium as a multi-in/out, 24-bit audio interface, with DI, re-amping, and MIDI functionality built right in.