We might be hijacking the thread, but there are good suggestions here. If you run stereo FX after the amp, you would need 2 XLR's to FOH to get the stereo signal. You only get the summed stereo signal when you use 1 1/4" main out jack.
I did live sound for a while back in the 80's. We never ran stereo mixes back then, because you can't get a good mix for various audience positions. It's hard enough get a decent eq for various positions without having to consider stereo as well. FI, if you run a stereo delay, the dry signal won't be as loud for people on one side, so the guitar part could sound off time. It seems like M/S mixes could be made use of live, but I wouldn't worry about all that. If you run 2 XLR's to FOH, the HE can sum them to mono or whatever is normally done at the venue.