A lower quality network streamer will (mostly) only affect that input. Any defects in a preamp will affect anything the DAC does. A network streaming card isn’t terribly expensive. A good preamp costs quite a bit. If the DAC proper is a cheap little chip then the DAC function and the preamp function can share the analog output cost effectively. At least in the case of the DS design, there’s no analog output circuitry that can be shared with a preamp.
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