Allthough considering ASR results this is very high level: changed NC400 to Purifi. If you don't have an NC400 already, go straight to a Purifi amp. Even if it's just for the gain setting. 80% of people don't even need then gain stage enabled if I had to guess. It's about 16dB SINAD for free!
Second, a dedicated DAC. I use my Denon 3700 vor movies and gaming, but for listening I switch to my SMSL Su-9n, and you notice the difference.
Plus a DAC let's your experiment with lots of stuff like filters and - the SMSL at least - let's you experiment with sound colors.
I'd say, if you don't notice changes in sound by upgrading your DAC or amp to a high quality one by ASR standards, your speakers are the bottle neck. If you have a speaker with low disortion, deep and reasonable flat FR and great resolution you should be able to have low, clean bass while also noticing differences between roll off filters or at least compressed vs. uncompressed music.