PlayScore 2 allows you to adjust the volume of each part in the music independently, and assign a different instrument to each staff.
Play-My-Part
Whatever part you sing or play, PlayScore 2 can play just that part on its own, or standing out from the others.
Music with one part per staff
From the Documents screen, open your score by tapping on the thumbnail
Tap the Staves
button lower left
Set the volume for each staff as you want it. The staff controls are arranged top to bottom as in the music. If you want a part to stand out but still hear the others, consider giving it an instrument such as clarinet
Music with two parts per staff
Some multi-part vocal music is written with two parts to each staff. This is common in barbershop quartets but can also be true of hymns and in musical theatre.
PlayScore 2 can separate parts when written 2-to-a-staff as long as they are printed stem-up/stem-down. For example if the soprano and alto parts are printed on the same staff, PlayScore 2 can separate them, as long as the soprano is printed with stems going up and the alto with stems going down.
From the Documents screen, open your score by tapping on the thumbnail
Tap the cogwheel
and set Staff voices to 2 (then close the control panel by tapping the cogwheel again). Note that in PlayScore 2 for Android this option is called Split Staves
Tap the Staves
button lower left
Set the volume for each part as you want it
Tap Done to return to the Play screen
Count-in (Apple devices only) – If you need a little time to pick up your instrument, tap the icon 2nd from the left at the bottom and select a number of Count-in measures