I stumbled across a simple way to improve sound of backing tracks. Export the song to midi, and open in the (free) program MidiClef (on my Android phone). From there you can choose instruments beyond those available in iRealPro. Then export audio from there to an acc file (the default). To my ears, the results are nicer to play to. This is especially true if experimenting with latin songs that use modern beats, but you want more folk instruments. e.g. Change piano in salsa beat to santur (a dulcimer).