I can recall a couple of occasions where an owner wrote off the amps onboard dac, prefering an external one.
In both cases, in an A/B comparison, the external dac was prefered, usual reasons, better resolution, focus etc, etc.
In both cases, replicating the test showed their to be a significant difference in level between the onboard and external dac, the internal being noticeably quieter, which of course makes it sound less 'good'.
I have also observed similar results using Apple's AEX, many suggesting that the dac is not very good, despite a perfectly decent chipset being used. The fact that the AEX outputs 1 volt whereas most dacs output twice that is rarely mentioned. When differences are very small, as they are between compedent dacs, level is everything.