When using USB-C iPhones/iPads, remember to turn the output volume to max on the device so that you can hear the playback from the device on the iRig Quattro I/O. The reason behind, on iOS devices, output from Lightning is a low impedance circuit while on an USB-C the output impedance is a bit high which the impedance matching on Quattro is old iPhone favor and has made the audio level to a headphone matched. This matching can be found on an USB-C Hub with Audio/Headphone output which a Resistor / Capacitor couple is built with the output channel.
Suggest IK to do some tuning or to update the bus impedance matching to solve the problem.
