I have an iPad Pro 12.9 (brand new). The audio works fine there, too, but I could not test the DAC's capabilities because I don't have software on the iPad that plays high resolution audio files, only Qobuz, and my subscription is only for CD-quality streaming. And Qobuz doesn't tell you what the app is actually sending to the headphones. My iPhone XS has a lightning connector, not USB-C, and I don't have a dongle that converts the lightning output to a useable form (a lightning to USB-C cable didn't give me any audible output).
On my MacBook Pro, Audirvana shows the capabilities of the connected DAC, as shown in the screen shot I posted earlier.
To find the USB-C 3.x generation cables, search Amazon for high-speed USB-C cables. I ordered one that does 5 Gbps (UGreen) and one that does 10 Gbps (NIMASO). The higher speed cables are intended for video connections, but I figured the price differential wasn't great and this way the cables are likely to be more useable for the future.
These cables all seem to come in 1m or 2m lengths. The short cables are just too short to comfortably and safely use with a laptop or iPad. Six feet is probably a bit too long, but at least they can be coiled.
When I get the new cables I'll be checking out the Morphit AU equalization, too, via the MacBook Pro.