I already have the DragonFly. It does sounds good, but does not work on Windows Vista (no volume controll). Neither does it have the push-buttons of the Calynx Coffee, or the RCA outputs.
The AudioEngine D1 I like as a device, but it does not have the vibrancy of the Calynx. I use the Calynx presently for a set of Ferrari reference headphones, but it's best suitable for driving low-power model of phone like Hifiman 300, or AKG various.
The AudioEngine D1 model works well driving an amp also (it's primary benefit), in my case a Stax 0007t, but like the Calynx, no DSDx2/DSD/SACD feature.
The FiiO Olympus is the best headphone (single purpose) amplifier I have discovered.
There are betters, I am confident. The Dragonfly is good enough for Audeze LCD-3.