XSUM-BB-03 Combo Breakout Box Connect this breakout box to the Multi-purpose I/O. This combination box has a set of 1/4" TRS jacks to use the additional Mix-B outputs and a set of 1/4" TRS jacks for a second set of Mix-A outputs. The Mix-A outputs on this Combo breakout box are "Pre" the X.Sum's master level control and can be used for connection to a monitor control system or external preamps.