This feature allows you to use another feature previously restricted to HMX DLC: the ability to mark which instrument has a solo for use with game goals and challenges involving instrument solos.

Only mark instruments that actually have solos, or allow Magma: C3 to determine it for you. Do not mark an instrument if it does not have a solo, as it will mess with the game should a goal be tied to that instrument.

Vocal percussion sections count as solos in this case.

Many thanks to AddyMilldike for finding and sharing this information!