How do you handle files with varying bit depths and bit rates? How about upsampling?

I'm curious. I have a few questions about DACs.

1. If you have files with varying bit depths and bit rates (some files being 16-bit/44.1 kHz, others being 24-bit/192 kHz and so on), do you adjust your DAC manually per song or do you just set it up to the highest rates you have available?
2. If upsampling—let's say from 16-bit/44.1 kHz to 24-bit/96 kHz—and I have my DAC set to 24-bit/96 kHz, do I still need to use software upsampling to 96 kHz in foobar2000 or similar players?
3. And if no is the answer to #2, what would you normally use software upsampling for? Is it only if you don't have a dedicated DAC? What if your built-in soundcard can support the higher frequency (24-bit/96 kHz) and you already have it set on your Windows sound settings?

Thanks so much. Just trying to learn more about this.