How to get into high end digital? (Feeding a DAC)

I am looking primarily at the Schitt Yggdrasil or the Topping D90.

• How does one feed those?
  
• I am assuming any sort of CD transport would output the bit stream?
  
• or… they get saved to file and played from some media player into the DACs.
  

Some example of what is commonly done would be great.

The system currently consists of:

• TT —> Audio Research PH2
  
• An old Nakamichi 5 disk CD player
• TV
• Audible Illusions line stage (New tunes on the way, but it still sound OK to me with the old tube in it)
  
• Prima Luna (with GoldenLion and TS KT-120 one the way… and I might I’ll get the VTL mono blocks 100w/ch serviced)
  
• Vandy 2C and Vandy sub
  

I also have a Home Theatre pre, which is Roon capable, on the way… So that maybe does some of this for me as well? 

But to be totally honest, the digital side is a bit of mystery to me.
I have always thought we plug in a CD player and the signal comes out. (Maybe with some nuance in DACs, clock jitter, and filtering to separate the higher end from the lower end products.)