Hi Chris,
Before 2 months (i had in mind to use the instrument input for the doublebass and the mic input for vocals),
i did a similar question to Rick Jones:
If we can take the output signal from one of the two channels, from the output "effects send", and send it alone to a mixing board of a PA system.
He answered me:
<<You can send either channel separately to a mixing board via the send outputs. The output impedance is relatively low, less than 10kOhm, so it should work for moderate cable runs.
If the cable needs to be very long,
put a direct box on the send output to convert it to low impedance. If the reverb is selected, there is no reverb in the effects send output.
The direct out has both signals mixed together and
it has reverb, if selected.>>
So, i think that there's no problem with 1/4 or XLR, except in the case that you will need to run very long cables. In the second case you have to use the XLR (combined) output because it is a low impedance output (less than 1000 Ohm), or convert every 1/4 effect send output to XLR with a DI box.
I hope it helps.