Ykk: I think you are a bit confused. The DAC chip inside any player provides an analog signal to the analog output stage, where it is amplified enough to provide enough voltage to drive a preamp's input section. Outboard DACs may or may not use different DAC chips than the Oppo, but it is the design of the output stage that has a big impact on sound quality. Well-regarded outboard DACs not only have high quality DAC chips, but also have well designed analog output stages (and power supplies, etc.). When you output a digital signal from the Oppo, you bypass both the Oppo's internal DAC chips and the Oppo's analog output stage.
Even with the best, SOTA DAC chips, an analog output stage designed to come in under a certain price point or that is just poorly designed will not sound as good as an even cheaper DAC chip that is used in a well-designed high end DAC with a good analog output stage.
Even with the best, SOTA DAC chips, an analog output stage designed to come in under a certain price point or that is just poorly designed will not sound as good as an even cheaper DAC chip that is used in a well-designed high end DAC with a good analog output stage.