I own a Shiit Brfrost and have for 5 years. It still works perfect.
1. Try new quality interconnects between the the DAC and the preamp input. Optical between the steamer, CD, might be a good idea.
This is a big one
2. RFI in the voltage line will wash out the digital quality. Try a cheap Furman power strip for a test. If improved, then go for power a conditioner. I suggest a tripp lite 1800w model it also compensates for low, or high voltage, noisy power which dramatically affects digital quality. My system is silent for hum or hiss at high volume.
Additional:
3. I use 10 gauge speaker wire. I got it on Amazon, oxygen free, works great for me.
All these suggestions are relatively cheap, but could make a huge difference. Each made my system sound better. Good luck.