What is the opinion of Reddit about the
SMSL SD 793II DAC Decoder DIR9001 PCM1793 OPA2134 Coaxial Optical Input Headphone AMP?

Nope, that won’t work. The only thing that comes out of that port is light. You need electrons.

Good news is you can use a cheap-ish headphone amp to do what you need:

http://www.amazon.com/SMSL-Decoder-DIR9001-PCM1793-Headphone/dp/B00OIUVDBS