MB is discontinued (last update more than 5 month ago). As an audiophile I prefer the clearly better sounding AIMP…
Welcome to the forum zupp.
It's a pity your introductory post contains two incorrect statements.
MusicBee is not 'discontinued' but still under continuous development.
The latest patch update even dates from yesterday.
MusicBee does not 'sound worse than Aimp'.
MusicBee is capable of bit-perfect playback (which is as good as it gets), and I am guessing Aimp is too.
So if you observe differences in sound quality, you probably have misconfigured one of them, or have set them playing at different volumes, or have some audio processing in the audio path.