Ok I got to thinking from the limited documentation I found my hunch seems to be correct.
The main out looks like it is a stereo unbalanced output not a mono output. Connecting that stereo output with a TRS to XLR straight through cable to the balanced input on the Crown amp would result near complete signal cancellation.
Try connecting to the monitor output and using the monitor send on the mixer to feed the Crown amp.
Below is what I pulled from the manual.
"Monitor Outputs
These 1/4" TS outputs are the final
output from the Monitor send mix-
ing bus. This feed may be used to
connect to an amplifier and speak-
er. Feeding the output from the
Monitor out to an amplifier (and
possibly an equalizer) and then
to a floor monitor speaker allows
artists to monitor their own instru-
ments or vocals whilst performing,
or an engineer to monitor the mix.
Main Outputs
This output will send the final stereo line level signal
from the main mix. The primary purpose of these
jacks is to send the Main signal to external devices
that may run in parallel with the mixer. This may in-
clude additional power amplifiers, other mixers, PA
systems, as well as a wide range of other possible
signal processors."
