I can't say this will fix the issue or not, but I like the use of this and it does seem to make the DAC/AMP sound a little better... its the ifi purifier3
https://ifi-audio.com/products/ipurifier3/
also, just a thought.... some confuse the fan noise... even if its a small amount of noise if you are using open headphones it could get into the ears... I have found it makes a difference if you listen with the amp standing on its side you need to have the amp on the left side... I know, it sounds crazy saying that, but by placing the amp to the left will also place the fan away from you... if the amp is on the right side the fan is facing you... play around with it and you should be able to see that there is a difference to the fan noise that way... hope this helps you out... in either case the ipurifier3 does make a difference for you, it should give you a blacker background