You're questions are valid, but difficult to answer. They're too general. Most of what you're asking, you really can only get from experience. If you said something like this: "I have DAC A and I'm looking to improve on (whatever quality). Its a much easier question to answer because there's a clear focus on what you're after.
I do see one thing that I may be able to help with. You talk about different DAC chips. Nothing wrong with that; the chip has an effect on SQ. But the digital portion of a DAC is only half of the equation. I see way too many people ignore the analog portion of the DAC. Even if 2 dacs are very similar on the digital half, they can sound very different depending on how different the analog stage is designed. For example, I like Ayre very much. Ayre digital products have the "Ayre" sound just like their amps and preamps. And that's because the same person designed all the components. Its just something to consider. You should be able to use your Peachtree gear as a reference to whatever new products you audition.
I do see one thing that I may be able to help with. You talk about different DAC chips. Nothing wrong with that; the chip has an effect on SQ. But the digital portion of a DAC is only half of the equation. I see way too many people ignore the analog portion of the DAC. Even if 2 dacs are very similar on the digital half, they can sound very different depending on how different the analog stage is designed. For example, I like Ayre very much. Ayre digital products have the "Ayre" sound just like their amps and preamps. And that's because the same person designed all the components. Its just something to consider. You should be able to use your Peachtree gear as a reference to whatever new products you audition.