Many of the UHD/4K Smart TVs Lack RCA or 3.5mm or HDMI Stereo Output to Connect With Home Theatre. For example, our reviewed Samsung NU7100 series UHD TV has only optical audio output. But our reviewed Sony DAV TZ145 has only stereo RCA audio input. In these cases, a digital coaxial to RCA converter is cheaper fix. However, 5.1 will have different kind of converter. Here is Digital Coaxial to RCA Converter Buying Guide.
What to Know About Digital Coaxial to RCA Converter?
It is actually possible to create own DAC circuit based on 32bit/384K PCM5102 DAC chip and DIR9001 from Texas Instruments. Sound quality produced by PCM5102 DAC is smooth with good dynamics. You can power such circuit from a single 3.7V LIPO battery. If you know some circuit works that is better than opting for China made digital coaxial to RCA converter :
RCA audio cables transmits analog audio signals from one medium to another via copper or similar metal wire. Whereas the optical is fiber optic based system. TOSLINK (read Toshiba Link) is the standardized optical fiber connector system which commonly used in consumer audio equipment. TOSLINK can not carry lossless versions of Dolby TrueHD or DTS-HD Master Audio.
I am not going in to complex, costly options such as 5.1 amplifier to convert optical audio to RCA or HDMI. The HDMI cable, connector itself complex matter.
Biggest universal issue of these cheap China digital coaxial to RCA converters is possibility audible hum, low volume etc. These are obvious side-effects of converting digital back to analog. The fix of hum is earthing the bodies of the devices related to sound, even not related but present closely.
Last but not the least, using a digital coaxial to RCA converter is the last option to connect to audio system. It is unreliable at so lower cost. As coaxial going towards slow death in consumer electronics, you probably need to think other options whenever possible. A costly amplifier will serve similar purpose but result likely to be better because of better circuit.