USB is heavily affected by electric noise from the source device, so USB cable makes a great difference.
Network is better because network cable is much less affected. This is why a Network Music Player is better.
Optical / Coaxial / AES makes the DAC slave to the clock of the usually inferior source device (e.g. PC), unless the DAC has a re-clock circuit. Transmitting 352kHz PCM or DSD128 is usually not possible. Optical also introduces additional jitter.