New to digital high-end, need help

I'm a long-time audiophile that ripped all my CDs to flac over the past year. I've been listening through Duets/Touch for office and casual use. I have not really had a high-end home system in 6 years. Now I'm building a high-end system that will use a digital/flac source.

I have Aerial 10t speakers and currently looking for a pre/amps (possibly Audio Research or Classe). I'm familiar with the arguments for SS or tubes, etc. I need help with the source/dac/volume control because, after all my research and reading, it feels like I still don't have a clue . . .

1.) I'm using a Squeezebox Touch connected with wifi. At what price point can I expect a DAC to make a dramatic difference? $500? $1,000? $3,000?

2.) I would consider bypassing a preamp/linestage for now and using a DAC with volume control (or similar setup)I use an iPad mini for the Touch remote at this point, but the volume can be finicky and I would like to use the volume control on DAC/preamp to limit the max while using the ipad.

3.) I have read the digital volume controls (such as Touch/iPad??) actually decrease resolution as the volume is decreased. Is this true? Does that mean the Touch volume should always be at 100%?? 75%?

4.) I've heard $60k systems and owned $20k systems (just to provide a reference point). Are digital files successfully used in that level of system? Can they sound as good as a quality CD source? If so, what caliber of equipment is necessary/desirable?

Thanks to anyone that can help me muddle through this process.