Originally Posted by hbphotoav
) (FOH needs to be able to mix) his show without redress if he actually needs a different gain structure in the middle of the show... 'cause you're sure not gonna want him with his hands on your APIs while you're recording it.
That's one excellent reason why.
Seriously, rent a good passive transformer splitter i.e. Jensen or Lundahl. One of you takes the transformer side, the other the direct side. Active splits like the Klark Teknik are fine too.
Then you let live sound do their thing while you do your thing.
Monitoring - you can't accurately monitor what you're recording over FOH because you will hear the sound of FOH and the room more than the sound the mic is capturing. Subtleties of mic placement and spill issues are mostly lost e.g. kick drums always tend to sound impressive over a big pa... even when what the mic is hearing is junk. Monitor off the Radar into a small desk of some kind (any kind really) and thru good closed back headphones or in-ears.
Plus you will almost certainly want to check your recording of sound-check while FOH is doing something else. FOH is not going to want to have to keep switching to your playback whenever you want to listen to something. That's assuming they're okay with 20 channels of line level signals in the first place...