Mixing wav-files from SD-card

Hi!
Congratulations and thank you for your very useful work on ESP32-audio.
I wonder how it is possible to mix up to 6 different wavefiles (16-bit 44,1kHz) located on an sd-card  and play them over MIDI with low latency. This should be possible with I2S and SD-MMC-mode. Could you PLEASE think of a solution?
Sorry for my English - I'm from Austria (not Australia... ;-)