Summary
Measured performance of the FX-Audio DAC-X6 is rather disappointing. It loses to similarly priced Fiio E10K and by a larger margin to Topping D30.
On the other hand, its physical build is far better than the Fiio E10 and even Topping D30. And its headphone output which never gets distorted regardless of its dial position, is able to drive difficult headphones like the Sennheiser HD650.
So if you want a DAC with headphone output for just pocket change, you have found it. The FX-Audio DAC-X6 provides a competent physical package, lots of inputs, and nice headphone amplifier.
As a pure DAC, my recommendation remains to buy the Topping D30. Yes, it costs more but just cut back on morning coffee for a few days and you can afford it!