The mixed section soli is voiced similiar to the saxophone soli. There is a great amount of flexibility of numbers of instruments and types of instruments that can be used. They provide colorful changes in texture and a "small group" feel within a big band setting. The problem with a mixed soli is found in balancing brass and woodwind instruments. This should be taken into account when writing them. See the two examples below.
NOTE: Because the trombone is in a high register and could overpower the mix, Chris Merz has the trombone using a cup mute.