No sound iPad lightning to USB DAC

I can't get audio signal from iPad mini (A1455, late 2012 year, 9.3.5 (13G36) ) AND from any of 3 recent iPhones (2x iPhone 6 + 1x iPhone SE) via lightning to my Proton Wavelength USB DAC (non powered) using Apple Lightning to USB 3 adapted, with power attached. Then to my Hegel integrated amplifier. Works without any problems directly from any of MacBooks USB outputs. I would appreciate any advice. Thank you.