The schematic you show is a very small part of the total schematic. It looks very similar as the MHZS output stage.
The best improvement you get by connecting the DAC output with a I/V resistor to the input of the tubestage on your schematic.
This is the same mod as on my shanling CD T 100se. I think the Cayin has the same DAC's.( pcm1792)
Now you have bypassed all the opamps in the analoge path.
It is better for me to explain if you have the full schematic and a PCB layout.
Connecting the DAC output direcly to a tube stage is the best mod i ever heart. The less parts the better the sound. And because there are a view parts left to use, you can take the best parts for it. Most there is then only one capacitor in the whole audiopath.
