A used Denafrips Terminator II or a used La Scala MKII.
Don't cut corners with the DAC. It's the core that the rest of the system revolves around.
You can gradually upgrade the rest of the system later, and you will be rewarded as you use better components that will better reveal the DAC true capabilities.
In the future you will also need a DDC to improve the quality and clocking of the input to the DAC. This brings a big lift to sound.
Good luck