In addition to the four master mix inputs, four separate mixes may be monitored using the main inputs and the three Insert jacks on Channels 1, 2, and 3.

features:
o 1/4", RCA, and XLR inputs
o  five 1/4" or 1/8" headphones with individual volumes
o  high gain for operation in noisy environments
o  four master mix inputs
o  insert jacks on channels 1, 2, and 3
o  1/4” JOIN jack connects two RA53b units together

additional reading:
Rolls RA53b manual (pdf)