Thanks fireon!
^using inexpensive miniature AT853 omnis, similar to Church audio or Naiant omnis.
Comments and clarifications I was working on as fireon posted above (your comments/questions are in bold italics)
add or enable the low filter pass (to the potential 3rd Omni mic)
^ I suggest low pass filtering the omni if you cannot, or choose not to space the directional pair wider than you otherwise would when using that pair alone. Doing so helps prevent the omni's contribution in the midrange and higher from making the stereo image narrower. It can also help reduce comb-filtering and phasiness which might arise from the omni not being spaced sufficiently far from the other microphones that it will be mixed in with.
Spacing the directional pair farther apart allows the omni to be used full range without collapsing the stereo image, and helps reduce the potential for problems when the channels are summed together. In that case the microphone array is designed to incorporate the omni's full range contribution. This will pickup more room and audience sound. You can still EQ shape the omni channel or low pass it, or do whatever works, all best decided by ear afterward to your preference. I like using my omni channels full range and that's one reason my arrays have as much spacing between the omnis, and between them and the other channels, that I'm able to manage.
Omni mic dead center on the mic bar
^
Nice to have symmetry, but won't matter at all if you low pass the omni. In that case you can put the omni anywhere, it just fits nicely in the middle. If running the omni full range it is acting as part of the near-spaced arrangement with the directional microphones at mid and high frequencies and you'll want to have it centered.
With wide-spaced omnis plus a stereo pair in the center, symmetry is nice but less important. I'll telescopically extend one omni less far out from the center than the other if I need to. Rather than only extending the opposite omni far enough to match, I'll extended it out as far as I can in order to get as much spacing between omnis that I can. I have a 3 point near-spaced arrangement in the center between the omnis and I don't alter its spacing, but I will alter the spacing between each omni and that center arrangement without qualms.
space the outside mic’s 2x the distance as normal w/ the same angle (ortf or din recommended) to speaker array (1 pair of mic’s just PAS)
If you like ORTF or DIN, keep using those angles. Space them further or not based on if you plan to low pass the omni or not as mentioned above. Generally, when adding a 3rd mic in the middle and using it full-range, you'll want to double the spacing between the outside pair, or increase the angle between them, or some combination of both. It generally makes more sense to increase spacing rather than increasing angle, otherwise the the pair end up pointing sideways far off-axis from the stage and PA.
With wide-spaced omnis, I like a coincident pair in the center more than a near-spaced pair. This sort of combines the best of both approaches. X/Y with super/hypercardioids works really well. (The 3-point arrangement I mentioned above that I use is actually a Mid/Side pair in the center, in combination with a pair of supercardioids angled +/- 45 degrees spaced about 12-15" or so to either side of center).
PAS works well in general for taping because it puts the microphones on-axis with the primary source of direct sound. The ">>improved PAS table<<" link in my signature line points to a TS thread with a table that helps figure the most appropriate spacing between a PAS pair, as determined by the angle between mics needed to point them at the stacks. It's a really good option for a running simple single near-spaced stereo pair. It also applies when using an omni in the center, and a bit more spacing can be added if possible when it is run full range. (I have enough complexity going on up there already and don't have an ability to change the angle of the near-spaced supercards working in conjunction with the M/S pair in the middle, leaving them at +/-45 degrees all the time)
trying running my Omni cap’s outside to see how this improves low end response vs my card cap or hyper caps (vs. buying a 3rd pair of additional mic’s)
^Best way to really figure it out is to give it a try. You'll get loads of bass, especially in comparison to the hypers. Maybe too much. Some EQ goes a long way in dialing it in. The recording with omnis are likely to have less upper midrange presence so you might want to play around with bumping up that range with EQ as well. If you run just the pair of omni's by themselves, spacing them 3' apart is a good arrangement. If you have another pair in the center you might even space them more if you can.
Things that I am “now” thinking:
it may be cheaper/easier to purchase a pair of dedicated mic’s to pick up the low end better (suggestions in sub $500 range?)?
Good sounding omnis can be had for less cost than good sounding directional mics. I like the miniature DPAs because the sound great, are weatherproof and are so small and light they are easy to support at wide spreads and I can do other unusual things with them. Other miniature lavaliere omnis can work similarly at less cost. "Normal sized" omnis work fine too, they just take a larger bar to support at wide distances. I'm sure other folks will post suggestions about what might work for you.
When taping more then 2 mic’s do you record at level or two lower then your main mic’s?
I set trims to achieve good levels and avoid clipping, then balance everything out later in the mix. The mix really needs to be determined afterward by ear, and that is one of the great flexibilities that comes from running more than two microphones in an array. The most appropriate mix level between channels is basically impossible to predict at the show. Actual trim settings between channels will depend on the sensitivity of the microphones. Even if the sensitivities are the same, you may find you need to turn down the trim on the omnis once the music starts and the subs kick in as there is far more energy present in the low frequencies and omnis will eat it up.
If running 2 pairs of balanced mic’s (outdoors or indoors) what is your recommend mic positions (let’s assume 1 pair is card’s or hypers, 1 pair is omni’s)?
As touched on above, I'd suggest trying the cards or hypers in X/Y in the center between omnis spaced 3' apart or more if easily achievable.