With back line equipment, it's usually best to use what is provided or completely bypass it. With a quick turnover of bands (my guess) it is best to stick with what works for you. Although you can finally try something new, doing so in front of a bunch of people can turn out to be a nightmare sound wise for you. Especially if you have no time to adjust it.
I have thought about just using their rig too, cause theyre probably most familiar with their own back line and are able to help me out more so then if I brought my own stuff. If if was using both the cabs I imagine it would be an easy fix to just turn off the amp and maybe re wire how I'm plugged in, no more than 10 seconds I bet