Hey George,
I'm also using a QU-24 and use 8 tracks of playback in a musical. The my then primary soundcard, a Motu UltraLite mk3 is resting on the shelf since the third show, haven't had even a tiniest glitch.
I was lazy, so I just used the first channels for USB, and plugged the wireless bodypacks starting from ch 9, but _theoretically_ if you tell Qlab to output audio to channels 17/18 on your QU16, it _should_ appear on St1, and so on upwards. But it's just thinking without having a QU nearby...
SM