notlos, I may be incorrect here but Lionstracs Mediastation has 2 built in file players which play midi files and MP3/Wav etc files. They can both be used at the same time and I can't remember if it's 16 or 32 track sequencer. Whilst a song is playing you can cue another on the same player or ready one for playing on player 2.
It's quite clever (when it works that is as mine was doa and had a mind of its own).
Does this sound like what Korg also has?