Anything that isn't mp3. I'm actually stunned people still use that codec. Willingly. AAC is just far superior. ALAC/FLAC for lossless can get quite large. Then there's the gorilla in the room: do most of these songs even get resampled properly when a new format is released? Atmos is all the rage but a lot of songs from the past that are now available in the codec sound off because the separation of instruments and sound is so far away from the original.
Your current system probably sounds like music from 1998, muddled and drowning in bass.