1, analog output is analog signal, coaxial and optical fiber output is digital signal, which needs to be decoded into analog signal. Which one is better depends on the lower-level decoding equipment such as coaxial and optical fiber. In addition, analog signals are vulnerable to interference and attenuation, and they are seriously disturbed in the case of long distance and large interference. Coaxial and optical fiber are digital signals, which have less interference, and optical fiber has the least interference, because they are optical signals.

2. The reason why the sound card you mentioned doesn't have 3.5 is mainly because the impedance of high-end headphones is high, so you usually connect a power amplifier. If the impedance of your earphone is not very high (below 32 ohms) and you don't need a power amplifier, you need to connect the rca interface to 3.5, because you need analog signals.

3. Ordinary active multimedia speakers are connected with analog signals. If it is coaxial, one is that the speaker has its own decoding, such as Logitech z5500, and the other is that it needs to connect an amplifier and then a passive speaker.