Is it actually the quality of the hardware that allows this or is it clever software signal processing that could in theory be applied to other phones if someone sufficiently clever was so inclined?
In the HTC 10 it has been designed as an end-to-end solution, with professionally tuned audio circuitry. It will capture 24-bit audio, it will upscale to 24-bit, with a high-quality DAC, as well as featuring a more powerful headphone amp, that will drive higher-quality, more demanding, headphones.
However, the greatest part of this new BoomSound Hi-Fi edition handset may be the headphones that come in the box. Where many manufacturers give you headphones that are average, HTC is bundling a Hi-Res certified in-ear headset in the box.