I would consider a used Schiit Yggdrasil. The Yggdrasil is a very good DAC for the ~$2K and performs very well for its class. I highly recommend getting up this far in the hierarchy of DACs to gain a significant sound quality jump.
Upgrading to a stand alone DAC
I have the upgrade bug..lol. I am considering purchasing a stand alone DAC as 60% of my listening is thru my CD player (NAD C568). This was purchased new 3 years ago for $799.00. My budget would be $1500. Rest of system is the Marantz Ruby KI integrated amp and the Reference 3A de capo speakers. Would I hear a significant difference at this price point?