If I could get a board of who I'll be taping I take that and the omni's and leave the cards at home
That combination works really well.
Upfront clarity and presence and detail filling the center of the image from the SBD.
Open, enveloping stereo immersion and ambience out to either side from the omnis.
So if I used a front and rear facing cardorid, I would want to pan both to center, correct?
Balance the front three channels first, that’s +90% of everything. Start with the omnis, balance them and eq if necessary. Then bring up the level of the forward facing cardioid until you find a good blend of all three. You can do some eq on the forward cardioid too if necessary. Don't worry about the bottom end of the cardioids, the omnis will take care of that completely, what is important in the cardioids is clarity. Play around with the level of the center forward facing cardioid in the mix. Sometimes a similar level to the omnis works best, sometimes less, sometimes more. You will hear it will "click" into place sonically when the balance is right. Sometimes it works with the center mic at a few significantly different levels it's just a matter of choosing which is best.
Once the front three channels are balanced, you can season things by bring in a touch of the rear facing microphone. In a stereo mix it provides some natural openness, ambience and crowd reaction. Often just enough level to make things sound natural, barely noticeable except in its absence. For a stereo mix I may automate the level to bring it up higher between songs when the crowd reaction and excitement is strong. Simplest is just to pan it center, but some pseudo-stereo techniques can spread it out (ideally it is decorellated in the left and right channels so it spreads out to both sides and is not centered in the mix).
In a surround mix the rear facing cardioid forms the surround channel and can be used at a higher level without conflicting with the front. It’s duplicated and routed to each of the surround speakers (and optionally decorellated between each surround speaker channel like using it with the 2-channel mix, though that is less important).
But I suggest the X/Y cardioid center to start. Bring the X/Y up after the omnis are balanced, with both cardioids panned to the center (or collapsed to mono using a stereo width panning control, which is the same thing), adjust their level as mentioned above, then play with increased center width by panning each outwards to left and right (or by increasing the stereo width on the panning control, same thing) until you get a nice even image a blend across the playback stage between speakers.