Well, that's the HW. As with video, the 16-bits went on further than just mere hardware limits.

When we talk software mixing, STE maxed out CPU at 8 channels 50kHz, here's an example: http://yerzmyey.i-demo.pl/YERZMYEY-Octopush_ATARI_STe.mp3

Even plain 520 ST can do a lot on this YM chip.

Amiga 500 on the other had could a bit of this but only with 12kHz samples, and no volume control per channel, also those pesky filters.

Amiga 1200/4000 could do same - as per much faster CPU, but... they still left the old audio 8-bit chip in it :/