Not sure about my iMac aux power but my MacBook Pro offers something like 1.25v for 4ohm headphones and something like 3volts for higher impedance with automatic ohm detectionI would return your dragonfly red as soon as possible. Its performance is extremely underwhelming given its cost: https://www.audiosciencereview.com/...rements-of-dacport-hd-and-dragonfly-red.5977/
The topping DX1 has more power and better SINAD, so it's vastly superior to the dragonfly red as long as you don't mind the form-factor.