Like HD, I have to wonder what "default setting" really means in your specific case. If you are to compare say the following:
Use analog input, stereo mode, disable YPAO and any other dSP functions such as sound modes etc., versus straight, direct, or pure direct, then there should be no or only very subtle audible difference.
If your "it changed the sound quality like night and day" was just t add hyperbole for forum talks, then fair enough, just keep in mind that if you have someone else to press that button, even subtle differences would very likely disappear, let alone night and day hyperbole.
I am not against keep going after dacs, preamps, amps and stuff at all, I have my fair share, but I think it is a good idea to keep in mind why we are doing it, and think logically, that just about anything that can affect sound quality are known, and verifiable, except how and what people's mind can imagine things. For example, as ADTG cited, if THD is as low as what the RX-A1060's and if frequency response is virtually flat in the audible range, then as long as the output is no near it's clipping point, you can also guarantee there will be no sound quality difference in apples to apples comparisons. If you push the gear to near its clipping point, then all bets are off.