Being able to pause the TOP output display would be another good feature so we can scroll down to see what else is running on the User CPU and check priorities.
When I do play around with TOP, ssh and Google-commands, I see things other than MPD running on my user CPU (3) and wonder if any could be moved to another CPU. Additionally, I try to find relevant processes that might be MPD/SQ-related; e.g. USB output; and then raise their priority.
Interestingly, I could not find an active IRQ on TOP that might represent USB output on my Pi4 (with 4xDSD music playing). On my full mobo with i7, I could always see the USB IRQ frequently popping up near the top of TOP.