But seriously, shouldn't a good computer with good software be a "good" source.
Yes, it should. Many here on the forum though will site the fact that it isn't necessarily "good enough". However, I personally am in the camp of "relying" upon the Schiit DAC (Gungnir or Yggdrasil) to essentially "do their job correctly" and, therefore, negate the need for an optimized source. In fact those Schiit DACs have an indicator referred to as the "buy better gear" light. If it's off during playback, what's the issue?