PSA: I had problems with a lot less power and noticeable attenuation from the headphone output of the Topping DX3 Pro+ after upgrading to Firmware 1.25. Downgrading back to 1.23 fixed the problem. Make sure you check your headphone output power levels, I'd be interested if anyone else ran into the problem.
Numbers: I used Sennheiser HD 700 headphones, and totally maxed out the power (0.0 db and High Gain mode on, and PC set to 100 volume) and it was barely loud enough. Whereas with 1.23 firmware, leaving it at around -5 db and Regular Gain, and PC set to 35 volume, is more than fine volume levels.
If you use your headphone jack, please test it and see if you also have this issue; I know I saw it. It was hard to track down what changed to cause this issue in my system.